U.S. patent application number 11/703802 was filed with the patent office on 2007-07-26 for cleanup method for optics in immersion lithography.
This patent application is currently assigned to NIKON CORPORATION. Invention is credited to Andrew J. Hazelton, Hidemi Kawai, W. Thomas Novak, Douglas C. Watson.
Application Number | 20070171390 11/703802 |
Document ID | / |
Family ID | 33303091 |
Filed Date | 2007-07-26 |
United States Patent
Application |
20070171390 |
Kind Code |
A1 |
Hazelton; Andrew J. ; et
al. |
July 26, 2007 |
Cleanup method for optics in immersion lithography
Abstract
A lens cleaning module is provided for a lithography system
having an exposure apparatus including an objective lens. The
system includes a scanning stage for supporting a wafer beneath the
objective lens. A cleaning module coupling with the lithography
system is provided for cleaning the objective lens in a non-manual
cleaning process.
Inventors: |
Hazelton; Andrew J.; (Tokyo,
JP) ; Kawai; Hidemi; (Palo Alto, CA) ; Watson;
Douglas C.; (Campbell, CA) ; Novak; W. Thomas;
(Hillsborough, CA) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
NIKON CORPORATION
Tokyo
JP
|
Family ID: |
33303091 |
Appl. No.: |
11/703802 |
Filed: |
February 8, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11237651 |
Sep 29, 2005 |
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11703802 |
Feb 8, 2007 |
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PCT/US04/10309 |
Apr 2, 2004 |
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11237651 |
Sep 29, 2005 |
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60462556 |
Apr 11, 2003 |
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60482913 |
Jun 27, 2003 |
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Current U.S.
Class: |
355/30 ;
355/53 |
Current CPC
Class: |
B08B 3/04 20130101; G03F
7/70341 20130101; B08B 3/12 20130101; G03F 7/70891 20130101; G03F
7/70925 20130101; G03F 7/70916 20130101 |
Class at
Publication: |
355/030 ;
355/053 |
International
Class: |
G03B 27/52 20060101
G03B027/52 |
Claims
1. A lens cleaning module for a lithography system having an
exposure apparatus including an objective lens, comprising: a
scanning stage for supporting a wafer beneath the objective lens;
and a cleaning module coupling with said lithography system is
provided for cleaning the objective lens in a non-manual cleaning
process.
2.-3. (canceled)
4. The lens-cleaning module of claim 1, wherein the cleaning module
includes a heating/drying module for drying the objective lens.
5. The lens cleaning module of claim 1, wherein said lithography
system is an immersion lithography apparatus.
6. The lens-cleaning module of claim 1, wherein said exposure
apparatus has a light source which emits light having a wavelength
of less than about 250 nm.
7. (canceled)
8. The lens-cleaning module of claim 1, wherein said cleaning
module comprises a fluid retaining wall carried by said scanning
stage and a cleaning fluid provided on said scanning stage and
retained by said fluid retaining wall for contacting the objective
lens.
9. The lens-cleaning module of claim 1, wherein said cleaning fluid
is ethanol.
10. (canceled)
11. The lens-cleaning module of claim 8, further comprising a
contact material for cleaning and cleaning fluid is distributed
between contact material and lens during operation.
12. (canceled)
13. A method for patterning semiconductor wafers by immersion
lithography to improve exposure quality comprising the steps of:
loading a semiconductor wafer on a stage of an immersion
lithography apparatus; filling a liquid between said wafer and an
objective lens of said immersion lithography apparatus; exposing
said semiconductor wafer to a light source having a wavelength of
less than about 250 nm; unloading said semiconductor wafer;
cleaning a surface of said objective lens after said exposure step
utilizing a non-manual lens cleaning module.
14.-15. (canceled)
16. The method for patterning semiconductor wafer by immersion
lithography according to claim 13, wherein said non-manual lens
cleaning module further comprising a contact material for cleaning
and cleaning fluid is distributed between contact material and lens
during cleaning operation.
17. A method for patterning semiconductor wafers by immersion
lithography to improve exposure quality comprising the steps of:
utilizing a non-manual lens cleaning module to clean the surface of
objective lens before water exposure processing; loading a
semiconductor wafer on a stage of an immersion lithography
apparatus; filling a liquid between said wafer and an objective
lens of said immersion lithography apparatus; exposing said
semiconductor wafer to a light source having a wavelength of less
than about 250 nm.
18.-19. (canceled)
20. The method for patterning semiconductor wafer by immersion
lithography according to claim 17, wherein said non-manual lens
cleaning module further comprising a contact material for cleaning
and cleaning fluid is distributed between contact material and lens
during cleaning operation.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a Division of U.S. patent application Ser. No.
11/237,651 filed Sep. 29, 2005, which is a Continuation of
International Application No. PCT/US2004/010309 filed Apr. 2, 2004,
which claims the benefit of U.S. Provisional Patent Application No.
60/462,556 filed Apr. 11, 2003 and U.S. Provisional Patent
Application No. 60/482,913 filed Jun. 27, 2003. The disclosures of
these applications are hereby incorporated by reference herein in
their entireties.
BACKGROUND
[0002] This invention relates to an immersion lithography system
and more particularly to methods, as well as systems, for cleaning
up the optical element that contacts and absorbs water in the
process of immersion lithography.
[0003] Immersion lithography systems, such as disclosed in
WO99/49504, which is herein incorporated by reference for
describing the general background of the technology as well as some
general considerations related thereto, are adapted to supply a
liquid into the space between a workpiece such as a wafer and the
last-stage optical element of an optical system for projecting the
image of a reticle onto the workpiece. The liquid thus supplied
improves the performance of the optical system and the quality of
the exposure.
[0004] The liquid to be supplied may be water for light with
wavelength of 193 nm although different liquids may be necessary
for light with other wavelengths. Because the last-stage optical
element of the optical system is exposed to the liquid, there is a
possibility that some of the liquid may be absorbed. This
possibility is particularly high if the last-stage optical element
of the optical system is a lens because calcium fluoride is a
common lens material for lithography systems while it is a
hygroscopic material that is capable of absorbing water from the
surrounding environment.
[0005] The absorbed water may cause several problems. First, it may
degrade the image projected by the lens by changing the refractive
properties of the lens or by causing the lens to swell to thereby
change the geometry of the lens. Second, it may cause long-term
degradation of the lens due to chemical effects.
[0006] Conventional air-immersion exposure lithography systems
require the optical elements to be made detachable for maintenance
work such as when they are cleaned. It is a cumbersome and
time-consuming operation, however, to remove an optical element and
to reset it after it is cleaned or to exchange an optical element
for a new one.
[0007] It is therefore an object of this invention to provide
systems and methods for periodically removing the water from the
lens such that the amount of absorbed water will not reach a
critical level and the degradation of the image and the long-term
damage to the lens can be prevented.
[0008] It is another object of the invention to provide systems and
methods for making the maintenance of the optical element of an
immersion lithography apparatus easier and thereby improve the
useful lifetime of the optical element.
SUMMARY
[0009] Immersion lithography apparatus of this invention may
include a reticle stage arranged to retain a reticle, a working
stage arranged to retain a workpiece, an optical system including
an illumination source and an optical element opposite the
workpiece for projecting an image pattern of the reticle onto the
workpiece by radiation from the illumination source while defining
a gap between the optical element and the workpiece, and a
fluid-supplying device for providing an immersion liquid between
and contacting both the optical element and the workpiece during an
immersion lithography process. The apparatus also includes a
cleaning device to clean the optical element. The term "cleaning"
will be used throughout this disclosure to mean both removing
immersion liquid that has been absorbed into the optical element
and removing dirt, debris, salts and the like from the optical
element.
[0010] Many different kinds of cleaning devices may be used within
the scope of this invention. For example, the cleaning device may
use a cleaning liquid having affinity to the immersion liquid to be
contacted with the optical element. If the immersion liquid is
water, ethanol may serve as the cleaning liquid. As another
example, the cleaning device may include a heat-generating device
for heating the optical element and/or a vacuum device for
generating a vacuum condition on the optical element.
[0011] Ultrasonic vibrations may be used for removing the absorbed
liquid. An ultrasonic vibrator such as a piezoelectric transducer
may be attached to the housing for the optical element or placed
opposite the optical element such that the vibrations may be
transmitted to the optical element through a liquid maintained in
the gap.
[0012] Alternatively, cavitating bubbles may be used for the
removal of the absorbed liquid. A pad with fins may be used to
generate cavitating bubbles in a liquid maintained in the gap
between the pad and the optical element.
[0013] According to another embodiment of the invention, the
nozzles through which the immersion liquid is supplied into the gap
between the workpiece and the optical element may be used to
alternately supply a cleaning liquid by providing a flow
route-switching device such as a switch valve.
[0014] With a system and method of this invention, the cleaning
procedure becomes significantly easier and faster because there is
no need to detach the optical element to be cleaned and the
cleaning process improves the useful lifetime of the optical
element.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The invention will be described in conjunction with the
following drawings of exemplary embodiments in which like reference
numerals designate like elements, and in which:
[0016] FIG. 1 is a schematic cross-sectional view of an immersion
lithography apparatus to which methods and systems of this
invention may be applied;
[0017] FIG. 2 is a process flow diagram illustrating an exemplary
process by which semiconductor devices are fabricated using the
apparatus shown in FIG. 1 according to the invention;
[0018] FIG. 3 is a flowchart of the wafer processing step shown in
FIG. 2 in the case of fabricating semiconductor devices according
to the invention;
[0019] FIG. 4 is a schematic drawing showing a side view of a
portion of the immersion lithography apparatus of FIG. 1;
[0020] FIG. 5 is a schematic side view of a portion of another
immersion lithography apparatus having an ultrasonic transducer
attached so as to serve as its cleaning device;
[0021] FIG. 6 is a schematic side view of a portion of another
immersion lithography apparatus having a piezoelectric cleaning
device below its optical system;
[0022] FIG. 7 is a schematic diagonal view of an example of a
piezoelectric device;
[0023] FIG. 8 is a schematic side view of a portion of another
immersion lithography apparatus having two mutually attached
piezoelectric planar members as the cleaning device;
[0024] FIG. 9 is a schematic side view of a portion of another
immersion lithography apparatus having a bubble-generating pad as
the cleaning device; and
[0025] FIG. 10 is a schematic side view of a portion of another
immersion lithography apparatus having a switching device
incorporated in the fluid-supplying device.
DETAILED DESCRIPTION OF EMBODIMENTS
[0026] FIG. 1 shows an immersion lithography apparatus 100 to which
cleaning methods and systems of this invention may be applied.
[0027] As shown in FIG. 1, the immersion lithography apparatus 100
comprises an illuminator optical unit 1 including a light source
such as an excimer laser unit, an optical integrator (or
homogenizer) and a lens and serving to emit pulsed ultraviolet
light IL with wavelength 248 nm to be made incident to a pattern on
a reticle R. The pattern on the reticle R is projected onto a wafer
W coated with a photoresist at a specified magnification (such as
1/4 or 1/5) through a telecentric light projection unit PL. The
pulsed light IL may alternatively be ArF excimer laser light with
wavelength 193 nm, F.sub.2 laser light with wavelength 157 nm or
the i-line of a mercury lamp with wavelength 365 nm. In what
follows, the coordinate system with X-, Y- and Z-axes as shown in
FIG. 1 is referenced to explain the directions in describing the
structure and functions of the lithography apparatus 100. For the
convenience of disclosure and description, the light projection
unit PL is illustrated in FIG. 1 only by way of its last-stage
optical element (such as a lens) 4 disposed opposite to the wafer W
and a cylindrical housing 3 containing the rest of its
components.
[0028] The reticle R is supported on a reticle stage RST
incorporating a mechanism for moving the reticle R in the
X-direction, the Y-direction and the rotary direction around the
Z-axis. The two-dimensional position and orientation of the reticle
R on the reticle stage RST are detected by a laser interferometer
(not shown) in real time and the positioning of the reticle R is
affected by a main control unit 14 on the basis of the detection
thus made.
[0029] The wafer W is held by a wafer holder (not shown) on a
Z-stage 9 for controlling the focusing position (along the Z-axis)
and the tilting angle of the wafer W. The Z-stage 9 is affixed to
an XY-stage 10 adapted to move in the XY-plane substantially
parallel to the image-forming surface of the light projection unit
PL. The XY-stage 10 is set on a base 11. Thus, the Z-stage 9 serves
to match the wafer surface with the image surface of the light
projection unit PL by adjusting the focusing position (along the
Z-axis) and the tilting angle of the wafer W by the auto-focusing
and auto-leveling method, and the XY-stage 10 serves to adjust the
position of the wafer W in the X-direction and the Y-direction.
[0030] The two-dimensional position and orientation of the Z-stage
9 (and hence also of the wafer W) are monitored in real time by
another laser interferometer 13 with reference to a mobile mirror
12 affixed to the Z-stage 9. Control data based on the results of
this monitoring are transmitted from the main control unit 14 to a
stage-driving unit 15 adapted to control the motions of the Z-stage
9 and the XY-stage 10 according to the received control data. At
the time of an exposure, the projection light is made to
sequentially move from one to another of different exposure
positions on the wafer W according to the pattern on the reticle R
in a step-and-repeat routine or in a step-and-scan routine.
[0031] The lithography apparatus 100 described with reference to
FIG. 1 is an immersion lithography apparatus and is hence adapted
to have a liquid (or the "immersion liquid") 7 of a specified kind
such as water filling the space (the "gap") between the surface of
the wafer W and the lower surface of the last-stage optical element
4 of the light projection unit PL at least while the pattern image
of the reticle R is being projected onto the wafer W.
[0032] The last-stage optical element 4 of the light projection
unit PL may be detachably affixed to the cylindrical housing 3 and
is designed such that the liquid 7 will contact only the last-stage
optical element 4 and not the cylindrical housing 3 because the
housing 3 typically comprises a metallic material and is likely to
become corroded.
[0033] The liquid 7 is supplied from a liquid supply unit 5 that
may comprise a tank, a pressure pump and a temperature regulator
(not individually shown) to the space above the wafer W under a
temperature-regulated condition and is collected by a liquid
recovery unit 6. The temperature of the liquid 7 is regulated to be
approximately the same as the temperature inside the chamber in
which the lithography apparatus 100 itself is disposed. Numeral 21
indicates supply nozzles through which the liquid 7 is supplied
from the supply unit 5. Numeral 23 indicates recovery nozzles
through which the liquid 7 is collected into the recovery unit 6.
The structure described above with reference to FIG. 1 is not
intended to limit the scope of the immersion lithography apparatus
to which the cleaning methods and devices of the invention are
applicable. In other words, the cleaning methods and devices of the
invention are applicable to immersion lithography apparatus of many
different kinds. In particular, the numbers and arrangements of the
supply and recovery nozzles 21 and 23 around the light projection
unit PL may be designed in a variety of ways for establishing a
smooth flow and quick recovery of the immersion liquid 7.
[0034] A method embodying this invention of removing the portion of
the liquid 7 such as water absorbed by the last-stage optical
element 4 made of a hygroscopic material, as well as dirt, debris,
etc., is explained next with reference to FIGS. 1 and 4. After the
wafer W is exposed with light from the illuminator optical unit 1
through the light projection unit PL in the presence of the liquid
7 as shown in FIG. 1, the liquid 7 is removed from underneath the
light projection unit PL and a cleaning device 30 is brought into
contact with the last-stage optical element 4 as shown in FIG. 4.
In the case of a portable kind, as shown in FIG. 4, the cleaning
device 30 may be placed on the Z-stage 9 or the aforementioned
wafer holder thereon, as shown in FIG. 4, in place of the wafer
W.
[0035] Different types and kinds of cleaning devices 30 can be used
for the purpose of this invention. As a first example, the cleaning
device 30 may be a container containing a liquid ("cleaning
liquid") having a strong affinity to the immersion liquid 7 that is
absorbed by the optical element 4. If the immersion liquid 7 is
water, the cleaning device 30 may contain ethanol because ethanol
has a strong affinity to water. Any cleaning liquid may be used
provided it has a sufficiently strong affinity to the liquid to be
removed and does not damage the optical element 4 or its coating.
The bottom surface of the optical element 4 is soaked in the
cleaning liquid for a period of time sufficiently long to reduce
the level of the absorbed immersion liquid. The cleaning device 30
is removed thereafter and the optical element 4 is ready to be
exposed to the liquid 7 again.
[0036] As another example, the cleaning device 30 may contain a
heat-generating device and/or a vacuum device (not separately
shown). The combination of heat and vacuum on the surface of the
optical element 4 causes the absorbed liquid to undergo a phase
change into vapor, or to evaporate from the surface. The reduction
in liquid density on the surface of the optical element 4 draws the
liquid 7 that is absorbed more deeply in the element 4 to the
surface of the optical element 4.
[0037] FIG. 5 shows a third example in which use is made of an
ultrasonic transducer (or ultrasonic vibrator) 32 attached to the
housing 3 of the light projection unit PL. As the ultrasonic
transducer 32 (such as a piezoelectric transducer) is activated,
pressure waves are generated and propagated, serving to clean the
surface of the optical element 4.
[0038] During the cleaning operation in FIG. 5, the gap adjacent to
the optical element 4 is filled with the immersion liquid 7. In
this case, the supply and recovery nozzles can continue to supply
and collect the immersion liquid 7, or the supply and recovery
nozzles can stop supplying and collecting the immersion liquid 7.
Also during the cleaning operation, the optical element 4 can face
a surface of wafer W, a surface of the Z-stage 9, or a surface of
another assembly.
[0039] FIG. 6 is a fourth example using a vibratory tool 34 placed
below the optical element 4 to be cleaned. The tool 34 may be
shaped like the wafer W with thickness more or less equal to that
of the wafer W, or about 0.5-1 mm, and may be made entirely of a
piezoelectric material such that its thickness will fluctuate when
activated. As the tool 34 is placed below the optical element 4,
like the wafer W as shown in FIG. 1, and the gap between the
optical element 4 and the tool 34 is filled with the liquid 7,
pressure waves are generated in the immersion liquid 7 to clean the
optical element.
[0040] During the cleaning operation of FIG. 6, the gap adjacent to
the optical element 4 is filled with the immersion liquid 7. In
this case, the supply and recovery nozzles can continue to supply
and collect the immersion liquid, or the supply and recovery
nozzles can stop supplying and collecting the immersion liquid 7.
In another example, the vibrator tool 34 may be a ultrasonic
transducer attached to the wafer holder on a Z-stage 9, or another
assembly.
[0041] FIG. 7 shows another tool 36, structured alternatively,
having a plurality of piezoelectric transducers 38 supported by a
planar supporting member 39.
[0042] FIG. 8 shows still another example of a cleaning device
having two planar members 40 of a piezoelectric material attached
in a face-to-face relationship and adapted to oscillate parallel to
each other and out of phase by 180.degree. with respect to each
other. As a result, these members 40, attached to each other, will
vibrate in the transverse directions, as shown in FIG. 8 in a very
exaggerated manner. The vibration has node points at constant
intervals where the members 40 are not displaced. The members 40
are supported at these node points on a supporting member 41. As
voltages are applied to these members 40 so as to cause the
vibrations in the mode described above, ultrasonic pressure waves
are thereby generated and propagated through the liquid 7, and the
optical element 4 is cleaned, as desired.
[0043] FIG. 9 shows still another example of a cleaning device that
cleans the optical element 4 by creating cavitating bubbles.
Cavitating bubbles trapped and energized by ultrasound are
high-temperature, high-pressure microreactors and intense energy
released by the implosive compression of the bubbles is believed to
rip molecules apart. The example shown in FIG. 9 is characterized
as comprising a pad 43 with fins protruding upward and rapidly
moved horizontally as shown by an arrow below the optical element 4
with a bubble-generating liquid 17 filling the gap in between
(structure for moving the pad 43 not being shown). As the pad 43 is
thus moved, the fins serve to stir the liquid 17 and to generate
cavitating bubbles that in turn serve to clean the optical
element.
[0044] FIG. 10 shows a different approach to the problem of
cleaning the last-stage optical element 4 by applying a cleaning
liquid on its bottom surface by using the same source nozzles 21
used for supplying the immersion liquid 7. For this purpose, a
switch valve 25 is inserted between the supply nozzle 21 and the
liquid unit 5 such that the immersion liquid 7 and the cleaning
liquid can be supplied selectively through the supply nozzle
21.
[0045] It is again noted that the cleaning methods and systems
according to this invention are applicable to immersion lithography
apparatus of different kinds and types, for example, having
different numbers of source nozzles. A switch valve as described
above need not necessarily be provided to each of the source
nozzles but may be provided to a group of the source nozzles.
[0046] The wafer W itself or a pad 18 of a suitable kind may be
placed below the optical element 4 to provide a suitable gap in
between when the cleaning liquid is thus supplied through the
supply nozzles 21. This embodiment of the invention is advantageous
because the same nozzles already present for supplying the
immersion liquid can be utilized for the cleaning process.
[0047] Although various methods have been separately described
above, they may be used in combinations, although that is not
separately illustrated in the drawings. For example, the pad 43
with fins shown in FIG. 9 may be used instead of the pad 18 of FIG.
10. In other words, the examples described above are not intended
to limit the scope of the invention, and many modifications and
variations are possible within the scope of this invention. For
example, a polishing pad similar to one used in chemical mechanical
polishing may be used for this purpose. The cleanup procedure shown
in FIGS. 4-10 may be carried out with ultraviolet light. The light
may irradiate the optical element 4. The light may be normal
exposure light from the illuminator optical unit 1 or some other
light of an appropriate wavelength for the purpose of the cleanup.
In another example, the ultraviolet light for the purpose of the
cleanup may be used without the cleanup procedure shown in FIGS.
4-10, and may be used under a condition in which the gap adjacent
to the optical element 4 is filled with the immersion liquid 7 from
the liquid supply unit 5. All such modifications and variations
that may be apparent to a person skilled in the art are intended to
be within the scope of this invention.
[0048] Any of the above described cleaning methods for removing
immersion fluid absorbed by the last-stage optical element also may
be used to remove salts, deposits, dirt and debris that may have
accumulated. The term cleaning therefore refers to both of these
phenomena.
[0049] FIG. 2 is referenced next to describe a process for
fabricating a semiconductor device by using an immersion
lithography apparatus incorporating a cleaning device embodying
this invention. In step 301 the device's function and performance
characteristics are designed. Next, in step 302, a mask (reticle)
having a pattern is designed according to the previous designing
step, and in a parallel step 303, a wafer is made from a silicon
material. The mask pattern designed in step 302 is exposed onto the
wafer from step 303 in step 304 by a photolithography system such
as the systems described above. In step 305 the semiconductor
device is assembled (including the dicing process, bonding process
and packaging process), then finally the device is inspected in
step 306.
[0050] FIG. 3 illustrates a detailed flowchart example of the
above-mentioned step 304 in the case of fabricating semiconductor
devices. In step 311 (oxidation step), the wafer surface is
oxidized. In step 312 (CVD step), an insulation film is formed on
the wafer surface. In step 313 (electrode formation step),
electrodes are formed on the wafer by vapor deposition. In step 314
(ion implantation step), ions are implanted in the wafer. The
aforementioned steps 311-314 form the preprocessing steps for
wafers during wafer processing, and selection is made at each step
according to processing requirements.
[0051] At each stage of wafer processing, when the above-mentioned
preprocessing steps have been completed, the following
post-processing steps are implemented. During post-processing,
initially, in step 315 (photoresist formation step), photoresist is
applied to a wafer. Next, in step 316 (exposure step), the
above-mentioned exposure device is used to transfer the circuit
pattern of a mask (reticle) onto a wafer. Then, in step 317
(developing step), the exposed wafer is developed, and in step 318
(etching step), parts other than residual photoresist (exposed
material surface) are removed by etching. In step 319 (photoresist
removal step), unnecessary photoresist remaining after etching is
removed. Multiple circuit patterns are formed by repetition of
these preprocessing and post-processing steps.
[0052] While a lithography system of this invention has been
described in terms of several preferred embodiments, there are
alterations, permutations, and various substitute equivalents which
fall within the scope of this invention. There are many alternative
ways of implementing the methods and apparatus of the
invention.
* * * * *