U.S. patent application number 12/041634 was filed with the patent office on 2008-07-03 for optical switching in lithography system.
Invention is credited to Remco Jager, Pieter Kruit, Johannes Christiaan van 't Spijker, Jan-Jaco Marco Wieland.
Application Number | 20080158536 12/041634 |
Document ID | / |
Family ID | 32176717 |
Filed Date | 2008-07-03 |
United States Patent
Application |
20080158536 |
Kind Code |
A1 |
Wieland; Jan-Jaco Marco ; et
al. |
July 3, 2008 |
OPTICAL SWITCHING IN LITHOGRAPHY SYSTEM
Abstract
A maskless lithography system for transferring a pattern onto
the surface of a target. At least one beam generator for generating
a plurality of beamlets. A plurality of modulators modulate the
magnitude of a beamlet, and a control unit controls of the
modulators. The control unit generates and delivers pattern data to
the modulators for controlling the magnitude of each individual
beamlet. The control unit includes at least one data storage for
storing the pattern data, at least one readout unit for reading out
the data from the data storage, at least one data converter for
converting the data that is read out from the data storage into at
least one modulated light beam, and at least one optical
transmitter for transmitting the at least one modulated light beam
to the modulation modulators.
Inventors: |
Wieland; Jan-Jaco Marco;
(Delft, NL) ; van 't Spijker; Johannes Christiaan;
(Delft, NL) ; Jager; Remco; (Delft, NL) ;
Kruit; Pieter; (Delft, NL) |
Correspondence
Address: |
BLAKELY SOKOLOFF TAYLOR & ZAFMAN
1279 OAKMEAD PARKWAY
SUNNYVALE
CA
94085-4040
US
|
Family ID: |
32176717 |
Appl. No.: |
12/041634 |
Filed: |
March 3, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11653107 |
Jan 11, 2007 |
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12041634 |
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10692632 |
Oct 24, 2003 |
6958804 |
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11653107 |
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60421464 |
Oct 25, 2002 |
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Current U.S.
Class: |
355/67 ;
355/53 |
Current CPC
Class: |
B82Y 10/00 20130101;
H01J 2237/0437 20130101; H01J 2237/2482 20130101; H01J 37/045
20130101; G03F 7/70508 20130101; G03B 27/52 20130101; H01J
2237/0435 20130101; G03F 7/70291 20130101; H01J 37/3174 20130101;
G03F 7/70825 20130101; H01J 2237/0432 20130101; B82Y 40/00
20130101; H01J 37/3177 20130101; G03F 7/70991 20130101; G03F
7/70383 20130101 |
Class at
Publication: |
355/67 ;
355/53 |
International
Class: |
G03B 27/54 20060101
G03B027/54; G03B 27/42 20060101 G03B027/42 |
Claims
1. A maskless lithography system for transferring a pattern onto
the surface of a target, comprising: a charged particle beam
generator generating a charged particle beam; a beam splitter
splitting said beam into a plurality of beamlets; an optical system
realizing said beamlets to be directed towards projection lenses
without common cross-over in said system; said system thereto being
provided with subsequent electrostatic arrays influencing said
beamlets; said projection lenses projecting said beamlets on to
said target, therein reducing the cross section of said individual
beamlets.
2. The system according to claim 1, in which modulating means for
modulating individual beamlets are included between said splitter
and said projection lenses.
3. The system according to claim 2, wherein said modulating means
includes an electrostatic modulator deflector array and a beam stop
array.
4. The system according to claim 1, in which a scanning deflector
array is provided, for deflecting individual beamlets in a first
writing direction over said target.
5. The system according to claim 4, in which the said scanning
deflector array and said projection lenses are positioned in
mutually close vicinity;
6. The system according to claim 1, wherein said scanning deflector
array and projection lenses are positioned in the system in close
vicinity to said target surface.
7. The system according to claim 1, wherein during writing, the
target surface moves with respect to the system in a second writing
direction.
8. The system according to claim 1, further comprising a modulation
array which comprises an array of modulators, wherein each
modulator is adapted for either deflecting a beamlet away from its
optical axis or letting a beamlet pass undeflected, which
undeflected beamlets pass towards said scanning deflector
array.
9. The system according to claim 8, wherein a deflected beamlet is
prevented from reaching the target.
10. The system according to claim 8, further comprising a beam stop
array between said modulation array and said deflector array,
wherein said beam stop is arranged for stopping beamlets deflected
away from the optical axis.
11. The system according to claim 1, wherein said modulator array
is controlled using modulated light beams, wherein each light beam
holds part of the pattern data for controlling one or more
modulators.
12. The system according to claim 11, wherein said light beams are
projected on said modulator array using an optical system.
13. The system according to claim 11, wherein a modulated light
beam from an optical fiber end is projected on a light sensitive
element of a modulator.
14. The system according to claim 13, wherein said light sensitive
elements are located in the vicinity of one ore more individual
modulators, and wherein said light beams are directed into the
virtual space column defined by said plurality of parallel
beamlets.
15. The system according to claim 13, wherein said optical fiber
end is part of an optical fiber for transmitting pattern data from
a control unit comprising said pattern data, towards said modulator
array.
16. The system according to claim 1, wherein said beam generating
means comprising a beam generator, a system for shaping the same
into a parallel beam, and a beam splitter for generating a
plurality of substantially parallel beamlets.
17. The system according to claim 1, wherein said beam generating
means comprising a beam generator, a system for shaping the same
into a parallel beam, and a beam splitter for generating a
plurality of substantially parallel beamlets, which beamlets are
directed to said modulation array.
18. The system according to claim 17, wherein beamlets are
maintained substantially parallel up to projection onto said
target.
19. The system according to claim 1, wherein said beam generator
comprises an electron beam generating means.
Description
[0001] The present application is a divisional of non-provisional
divisional U.S. patent application Ser. No. 11/653,107, filed Jan.
11, 2007, which is a non-provisional divisional of U.S. patent
application Ser. No. 10/692,632 filed Oct. 24, 2003, now U.S. Pat.
No. 6,958,804 issued Oct. 25, 2005, which claims priority from U.S.
Provisional application No. 60/421,464 filed Oct. 25, 2002.
BACKGROUND
[0002] Lithography systems, including ion, laser, EUV and electron
beam systems, all require means to process and deliver a pattern to
some kind of writing means. A well known way to accomplish this is
by using a mask, and projecting this mask onto a substrate. As the
resolution becomes smaller and smaller, these masks have become
more difficult to produce. Furthermore, the (optical) means for
projecting these masks have become very complex.
[0003] A way of to overcome this problem is by using maskless
lithography.
[0004] Maskless lithography systems can be divided in two classes.
In the first class the pattern data are sent towards the individual
radiation source or sources. By tuning the intensity of the sources
at the right times, a pattern can be generated on the substrate,
which is most often a wafer or a mask. The switching of sources may
get problematic when the switching speed increases, for instance
due to a settling time or a source, which can be too long.
[0005] The second class of maskless lithography systems on the
other hand comprises either continuous sources or sources operating
at constant frequency. The pattern data are now sent towards
modulation means, which completely or partly stop the emitted beams
from reaching the target exposure surface when necessary. By
controlling these modulation means while moving over the target
exposure surface, a pattern is written. The modulation means are
less critical for settling times. A lot of maskless lithography
systems designed to achieve a higher throughput are therefore using
modulation means.
[0006] In U.S. Pat. No. 5,834,783, U.S. Pat. No. 5,905,267 and U.S.
Pat. No. 5,981,954, for instance, a maskless electron beam
lithography system with one electron source is disclosed. The
emitted electron beam is expanded, collimated and additionally
split by an aperture array into a plurality of beamlets. A blanker
array fed with pattern data stops the individual beamlets when a
control signal is given. The obtained image is then reduced by a
reduction electron optical system and projected on a wafer.
[0007] In US-A-1-20010028042, US-A-1-20010028043,
US-A-1-20010028044, WO-A1-02/054465, WO-A1-02/058118 and
WO-A1-02/058119, a maskless electron beam lithography system using
a plurality of electron sources is disclosed. The emitted electron
beamlets pass a blanker array, which deflects the individual
electron beamlets when the appropriate control signal is given. The
electron beams are shaped by a shaping array, and focused on a
wafer.
[0008] In WO-01/18606 and U.S. Pat. No. 6,285,488 an optical
lithography system is disclosed which uses a spatial light
modulator (SLM) to modulate a light beam. A light source emits
light pulses directed towards the SLM. The SLM comprises an array
of deformable mirrors, which reflect the emitted beam towards a
substrate or towards a beam stop structure depending on a control
signal sent to the mirror involved.
[0009] The current invention is based on the following insight and
understanding of the fundamentals of lithography.
[0010] A mask is a highly efficient way to store a pattern, the
amount of raw data to describe a pattern is enormous. Moreover, for
a commercially acceptable throughput, the data must be transported
towards the writing means at a very high data rate. Additionally
the high data rate must be obtained within limited space. It was up
to now not recognized that improvement of the data path in maskless
lithography systems has a profound effect on the through-put of
these Systems.
[0011] The information on a mask is normally used to transfer a
pattern from the mask on a certain area on the target exposure
surface. This area is called a die. To get an idea of the amount of
data that has to be transferred, imagine a die of 32 mm by 26
mm.
[0012] Now consider that somebody wants to write a pattern with a
critical dimension (CD) of 45 nm. Then there are 4.1*10.sup.11
CD-elements on a die. If each CD element consists of at least 30*30
pixels to satisfy the requirements, and if there is only one bit
needed to represent the intensity of said pixel, the information
present on a mask is represented by about 3.7*10.sup.14 bits. Say a
commercially acceptable throughput for a maskless lithography
system is about 10 wafers/hr. If there are 60 dies on a wafer, 60
times 3.7*10.sup.14 bits have to be transported towards the
modulation means per wafer. So 600 times 3.7*10.sup.14 bits have to
be transported towards the modulation means in 3600 seconds to get
the desired throughput. This corresponds to a data transfer rate of
about 60 Tbit/s!
[0013] In all mentioned systems the control signals are sent
electronically towards the modulation means. However, the bandwidth
of a metal wire is limited. The limit on the bandwidth of an
electrical interconnect is related to the maximum total capacity of
an electrical interconnect B.sub.max, to the overall cross-section
A and the length of the electrical interconnect L in the following
way:
B.sub.max=B.sub.0*(A/L.sup.2)
[0014] The constant of proportionality B.sub.0 is related to the
resistivity of copper interconnects. For typical multichip module
(MCM) technologies B.sub.0 is about 10.sup.16 bit/s. For on-chip
lines its value is about 10.sup.16 bit/s. The values are almost
independent on the particular fabrication technology.
[0015] The limit on the bandwidth of the electrical interconnect is
furthermore independent of its configuration. Whether the
interconnect is made up of many slow wires or a few fast wires up
to the point where other effect start to limit the performance
makes no difference.
[0016] The desired total capacity of the electrical interconnect is
100*10.sup.12=10.sup.14 bit/s. This corresponds to a ratio of the
overall cross-section to the square of the length of the electrical
interconnect or 10.sup.-1 in the case of a MCM and 10.sup.-2 in the
case of an on-chip connection. So if L is 1 m., the overall
cross-section of the copper that is needed is 0.01-0.1 m.sup.2 !
Compare that number with the size of a die that is written, which
is 0.0008 m.sup.2, and it is evidently impossible to establish the
data transfer without a demagnification of at least 10 after the
pattern information is added to the light beam.
[0017] Another approach to visualize the problem is to use the
typical speed of an electrical interconnect, which is in the order
of 1 Gbit/s. So to transfer 100 Tbit/s, 100,000 copper wires are
needed! This takes an enormous amount of space and is difficult to
handle.
SUMMARY OF THE INVENTION
[0018] An objective of the current invention is to improve the
systems described above.
[0019] A further objective of the current invention is to increase
the throughput of a maskless lithography system.
[0020] A further objective or the current invention is to reduce
the sensitivity of the lithography system with respect to all kinds
of (electromagnetic) disturbances.
[0021] A further objective of the current invention is to reduce
the space needed for transferring pattern data into the lithography
system.
[0022] A further objective of the current invention is to increase
design flexibility of the system.
[0023] The invention therefore provides a maskless lithography
system for transferring a pattern onto a surface of a target,
comprising: [0024] at least one beam generator for generating a
plurality of beamlets; [0025] a modulation means comprising a
plurality of modulators for modulating the magnitude of a beamlet
and [0026] a control unit for controlling each modulator, [0027]
wherein the control unit generates and delivers pattern data to
said modulation means for controlling the magnitude of each
individual beamlet, the control unit comprising: [0028] at least
one data storage for storing the pattern data; [0029] at least one
readout unit to read out the pattern data from the data storage;
[0030] at least one data converter for converting the pattern data
read out from the data storage into at least one modulated light
beam; [0031] at least one optical transmitter for transmitting said
at least one modulated light beam to said modulation means.
[0032] Using optical data transportation in a lithography system
makes it possible to create a maskless lithography system based on
known technology, but having an increased though-put. Furthermore,
it is possible to reduce the area needed. Furthermore, optical
transmission offers additional freedom for designing the layout of
the lithography system.
[0033] The radiation source that can be used in the beam generator
can emit any kind of radiation like electrons, positrons, x-rays,
photons or ions. The source is either a continuous source or a
source that is pulsed with a continuous frequency. The source
therefore does not generate any information. However, the purpose
of a lithography system is to pattern a certain target exposure
surface. Since the source does not provide any pattern data or
pattern information, the pattern information has to be added to the
beamlets somewhere along their trajectory by modulation means. It
should in this invention be realized that the pattern information
is transported using an optical system. The pattern information is
used to control modulation means which modulates beamlets which
actually write the pattern into a resist or in another way transfer
the pattern onto a sample, for instance a semiconductor wafer. In
the system, the nature or the pattern writing beamlets depends on
the nature of the source. In fact, the modulated light beam is a
pattern information carrying light beam, and the beamlets are
pattern writing beamlets.
[0034] In an embodiment, the beam generator has only one source,
and the lithography system has only one beam generator. In this
way, it is easier to control the inter beamlet homogeneity of the
system.
[0035] The modulation means can operate in different ways and be
based on various physical principles, depending on the nature of
the beamlets used for writing the pattern. It may generate a signal
which results in the activation of some blocking mechanism which
stops the beamlet, for instance a mechanical shutter or a crystal
becoming opaque due to electro-acoustic stimulation. Another
possibility is that to have the modulation means selectively
generate a signal, which results in the activation of some sort of
deflector element, like an electrostatic deflector or a mirror.
This results in a deflection of the selected irradiated beamlet.
The deflected beam is then projected on a blanker element, for
instance a beam absorbing plate provided with apertures, aligned
with the deflectors of mirrors. In both cases a commercially
satisfactory throughput can only be acquired when the beamlet
modulation is done very fast, preferably with a frequency of 100
MHz or more.
[0036] In maskless lithography systems the pattern information or
pattern data is represented by computer data, generally digital
computer data. The pattern data is partially or completely stored
in the data storage of the control unit. The control unit therefore
comprises a data storage medium, e.g. RAM, hard disks or optical
disk. This data is stored in a format that can be used to control
the modulation means in such a way that a predetermined pattern can
be repetitively generated. Furthermore, the control unit comprises
means to read out the data at a high data rate, To establish the
high data rate the control unit comprises an element that converts
the data into at least one pattern data carrying light beam. In an
embodiment, this data converter a vertical cavity surface emitting
laser (VCSEL) diode. If a bit is one, a light signal is emitted
while no light is sent out if the value of the bit equals zero. By
reading out a sequence of bits, a pattern information carrying
light beam is created. The pattern information carrying light beams
are then transported towards the modulation means. There are
several possible carriers that can realize the data transfer. In an
embodiment, parallel data storage means are used which are read out
almost simultaneously in order to obtain the data rate
required.
[0037] In an embodiment the transfer from the converter element in
the control unit a region close to the modulation means achieved
using optical fibers for the data transport. This allows flexible
data transport with minimal disturbance by electromagnetic fields
and other means. Furthermore, at allows the control unit to be
located remote from the rest of the lithography system, for
instance between 2-200 meters away from the rest of the system.
[0038] Currently, optical fibers that are used in telecom and
Ethernet applications are optimized for specific wavelengths,
predominantly 850, 1300 and 1500 nm. The 850 nm optimization is
established due to the good availability of the standard
InGaAs/GaAs laser diodes. The infrared wavelengths are used because
of the low fiber transmission losses, typically smaller than 0.4
dB/km. Future developments aim for wavelengths of 660 and 780 nm.
The lower wavelengths are preferred for the present invention
because of fewer diffraction related limitations at these
wavelengths. However, in some configurations larger wavelengths are
desired. The wavelengths that can be used in the present invention
range from about 200 to 1700 nm. Current developments furthermore
make it possible to transfer multiple signals through one channel.
For this purposes either multi-wavelength or multi mode optical
fibers are developed, and multiplexing/demultiplexing techniques
are used. Preferably, for the wavelength of the modulated light
beams is selected in an area which interferes as little as possible
with the beamlets and with the rest of the system. This allows the
optical transmitter to be designed almost independently from the
rest of the lithography system.
[0039] In an embodiment of the invention, each modulator or the
modulation means comprises a light sensitive element for converting
said at least one modulated light beam coming from said control
unit into a signal for actuating said modulator. In this way, the
optical transmitter can be kept small. The transfer rates can be
very high, and the modulator can for instance be made using
lithographic technologies. In a further embodiment thereof, said
optical transmitter comprise at least one optical fiber having a
modulation means end and a control unit end, for transmitting said
at least one modulated light beam from said control unit to said
modulation means.
[0040] In an embodiment, the lithography system comprises at least
one projector for projecting said at least one modulated light beam
on said modulation means. In this way, it offers an even greater
freedom of design. Furthermore, interference can be reduced.
[0041] In an embodiment with optical fibers, said at least one
optical fiber at its modulation means end is coupled to one or more
optical fiber arrays. In a further embodiment thereof,
substantially each optical fiber from said one or more optical
fiber arrays is coupled to one of said light sensitive converter
elements.
[0042] In an alternative embodiment, said at least one optical
fiber at its modulation means end is coupled to one or more optical
waveguides, and said optical waveguides being coupled to the light
sensitive elements.
[0043] In an embodiment of the maskless lithography system
described above, said optical transmitter comprises at least one
multiplexer at its control unit end and at least one demultiplexer
at its modulation means end.
[0044] In another embodiment of the maskless lithography system
described above, the system has an optical path parallel to which
said plurality of beamlets are traveling, wherein said optical
transmitter is furthermore provided with optical coupler for
coupling said at least one modulated light beam into said optical
path.
[0045] In embodiment described above, the data converter and the
optical transmitter is adapted for generating at least one
modulated light beam having at least one wavelength between 200 and
1700 nm. This wavelength was found to interfere as little as
possible with the rest of the system. Furthermore, it allows use of
many of-the-shelf components used in optical telecommunication
applications.
[0046] In a further embodiment of the invention, each light
sensitive element is provided with a selection filter which is
transparent for a predetermined wavelength range, or a selection
filter for transmitting light having a predetermined direction of
polarization, or a prism which limits the sensitivity of said light
sensitive element to light entering said prism from a predetermined
direction, or a grating which limits the sensitivity of said light
sensitive element to light entering said grating from a
predetermined direction. In this way, x-talk can be reduced.
[0047] In a further embodiment of the maskless lithography system
comprising optical fibers, said light sensitive element comprises a
photodiode, in an embodiment a MSM-photodiode, a PIN-photodiode or
an avalanche photodiode.
[0048] In an embodiment of the maskless lithography system with an
optical fiber array, the modulator comprises an electrostatic
deflector. Especially when the beam is a charged particle beam,
this allows easy modulation, using parts which are well known in
other fields of technology.
[0049] In an embodiment of the maskless lithography system
according to the present invention, the data converter comprises a
laser diode.
[0050] In an embodiment, the optical transmitter comprises at least
one optical fiber having a modulation means end and a control unit
end, for transmitting said at least one modulated light beam from
said control unit to said modulation means, and at least one
projector for projecting said modulation means end of said optical
fiber or optical fibers on said modulation mean. In this way, a
flexible design of the system is possible, both in lay-out and in
choice of components.
[0051] In an embodiment, each modulator of the modulation means
comprises a light sensitive element for converting said at least
one modulated light beam coming from said control unit into a
signal for actuating said modulator, and said modulation means has
a beam generating means side and a target side.
[0052] In an embodiment, each of said modulators comprise at least
one electrostatic deflector, an aperture between said at least one
electrostatic deflector and said target side, said electrostatic
deflectors of said modulators defining an electrostatic deflector
array and said apertures of said modulators defining an aperture
array.
[0053] In a further embodiment, each electrostatic deflector is
operationally coupled to a light sensitive element.
[0054] In this embodiment, said optical transmitter comprises at
least one beam splitter for splitting said at least one modulated
light beam into a plurality of modulated light beams.
[0055] In a further embodiment, the optical transmitter comprises
projectors for projecting said plurality of modulated light beams
on said light sensitive elements.
[0056] In this embodiment, said projector are adapted for
projecting at an angle between 0 and 88 degrees relative to a plane
perpendicular to said electrostatic deflector array. In this
embodiment. In a further embodiment, the projector comprises at
least one lens for projecting the plurality of modulated light
beams on said electrostatic deflector aperture array.
[0057] In an embodiment, the projector comprise a first demagnifier
with a reduction optical system for demagnifying the plurality of
modulated light beams and a projection optical system for
projecting the demagnified plurality of modulated light beams on
said electrostatic deflector aperture array. In an embodiment
thereof, said reduction optical system comprises a micro lens
array, each micro lens of said micro lens array being aligned with
one of said plurality of modulated light beams and adapted for
reducing the size of said one of said modulated light beams. In a
further embodiment thereof, said projection optical system further
comprises a mirror, for reflecting the plurality of modulated,
demagnified light beams coming from the reduction optical system in
the direction of said lens of the projection optical system.
[0058] In an embodiment of the electron beam maskless lithography
system described above, the area on the modulation means not
covered by the light sensitive elements is provided with a
reflective layer.
[0059] In an embodiment of the electron beam maskless lithography
system described above, a diffusive layer is provided on the
surface of the modulation means facing the incoming plurality of
modulated light beams.
[0060] In an embodiment, said optical transmitter further comprises
an optical waveguide for coupling each of the plurality of
modulated light beams substantially parallel to the electrostatic
deflector aperture array plane towards its corresponding light
sensitive element. In a further embodiment thereof, the optical
transmission means further comprises an optical micro lens array
provided with a plurality of micro lenses, each micro lens being
aligned with one of said plurality of modulated light beams for
coupling its modulated light beam into a corresponding optical
waveguide.
[0061] In an embodiment, the optical transmitter comprises a
plurality of optical fibers, the data converter means comprising
means for coupling said at least one modulated light beam in said
plurality of optical fibers, said plurality of optical fibers being
grouped to form at least one fiber ribbon, said at least one fiber
ribbon being attached at one of the sides of said electrostatic
deflection array, and the light sensitive elements being adapted
for electrically activating their corresponding electrostatic
deflector via electrical interconnects.
[0062] In another embodiment, the maskless lithography system, the
generating means comprise light beam generating means. In an
embodiment thereof, the light generating means are adapted for
generating a light beam having a wavelength smaller than 300 nm. In
a further embodiment thereof, the modulation means comprises a
spatial light modulator. In a further embodiment thereof, the
spatial light modulator comprises a deformable mirror device,
comprising an array of micro-mirrors. In yet a further embodiment
thereof, each micro-mirror comprises a light sensitive element
mounted on its backside coupled to said optical transmission means
for receiving a modulated light beam.
[0063] The invention further relates to a process wherein a
maskless lithography system is used described above.
[0064] The invention further relates to a method for transferring a
pattern onto the surface of a target using a lithography system
comprising beam generator for generating a plurality of beamlets
and modulation means for individually controllably modulating
substantially each beamlet, said method comprising: retrieving
pattern data from data storage; transforming said pattern data into
at last one modulated light beam; optically coupling said at least
one modulated light beam to said modulation means.
[0065] In an embodiment of this method the modulation means
comprise an array of modulators, each provided with light sensitive
elements, and method further comprises: directing said at least one
modulated light beam onto said modulators; coupling each of said
modulated light beams to one light sensitive element.
DRAWINGS
[0066] The invention will be further elucidated in the following
embodiments of a maskless lithography system according to the
current invention, in which:
[0067] FIGS. 1A, 1B a an operation scheme of part of the system of
the invention,
[0068] FIGS. 2A, 2B, 2C free space optical coupling,
[0069] FIGS. 3A, 3B illumination schemes of a modulation means,
[0070] FIG. 4 projection of optical fiber array on modulation
array;
[0071] FIGS. 5A, 5B projection systems for projecting a pattern
information carrying light beam on modulation means,
[0072] FIGS. 6A-6D illuminating schemes for the light sensitive
elements,
[0073] FIG. 7 coupling of pattern information carrying light beams
to light sensitive elements,
[0074] FIG. 8 top-view or FIG. 7,
[0075] FIG. 9 optical coupling using optical fiber ribbons,
[0076] FIG. 10 modulation means for an electron beam lithography
system,
[0077] FIG. 11 free space coupling of pattern information carrying
light beams to modulation means,
[0078] FIG. 12 illumination scheme of a modulation means,
[0079] FIG. 13 maskless optical lithography system,
[0080] FIG. 14 projection of fiber ends on modulation means
DETAILED DESCRIPTION OF THE INVENTION
[0081] Since the modulation means are fed with an optical signal,
they each comprise a light sensitive clement, preferably a
photodiode. The basic operation of the modulation means is
schematically shown in FIG. 1A. FIG. 1a schematically shows the
basic operational steps performed by the modulation means. Each
modulation means is provided with a light sensitive element,
preferably a photodiode, to be able to receive an optical
signal.
[0082] If the light sensitive element receives light, a signal is
generated and sent to modulator. As a result the passing beamlet
will be modulated and not reach the target exposure surface. If
there is no light, there is no signal transferred to the modulator.
The beamlet passes undisturbed, and finally reaches the target
exposure surface. By moving the target exposure surface and the
rest of the lithography system relative to each other while sending
pattern information towards the modulation means, a pattern can be
written.
[0083] It is of course also possible to operate the whole system in
the opposite way as shown. In FIG. 1B. In this case light falling
on the light sensitive element results in the cancellation of the
signal sent towards the modulation means. The passing beamlet will
reach the target exposure surface without any modulation. However,
when the light sensitive element does not receive light, a signal
is sent towards the modulation means, which prevents the passing
beamlet from reaching the target exposure surface.
[0084] The attachment of the optical fibers to the modulation means
can give serious complications. In an embodiment of the present
invention, the last part or the data trajectory therefore uses a
different transfer medium. In the latter case the fibers terminate
closely packed thus forming an optical fiber array. The emitted
pattern information carrying light beams are then sent towards
other optical carriers. When the modulation means are located in a
vacuum, it might be preferable to keep the optical fibers outside
the vacuum. In this case the emitted light beams can for instance
couple into the lithography system via a transparent part of the
vacuum boundary.
[0085] In most cases it is not practical to bring the pattern
information carrying light beams all the way to the light sensitive
elements through optical fibers. In that case other optical
carriers can continue the data transfer. Preferably the optical
fibers are bonded together to form an optical fiber array. The
pattern information carrying light beams then travel towards the
light sensitive elements in a different way. One possible way of
data transfer is to send the light emitted from the fibers towards
the light sensitive elements of the modulation means through the
same environment as wherein the irradiated beamlets are traveling.
In this way free space optical interconnects are created. Another
possible transport medium is an optical wave-guide, which is
located in the structure of the modulation means.
[0086] In the case of an optical wave-guide or an optical fiber,
multiple wavelengths can be transported through the channels as is
commonly done in telecommunication applications. The space occupied
by the transfer medium then reduces significantly, because several
pattern information carrying light beams share the same channel.
The conversion towards a signal that can be used by the modulators
can be made with an opto-electronic receiver, like a DWDM
multi-wavelength receiver.
[0087] The light sensitive element can be any element known in the
art that converts an incoming light signal into any other kind of
signal, like an electric or an acoustic signal. Examples of such
converters are photo cathodes, phototransistors, photo resistances
and photodiodes. In order to meet the high data rate requirements,
the light sensitive element should have a low capacitance, enabling
it to operate at a high frequency. Moreover the element is
preferably easy to integrate in the modulation means. There are
photodiodes that meet the demands mentioned above. The preferred
embodiment uses an MSM-photodiode. The main advantage of this
photodiode is its low capacitance. It is therefore able to operate
at a high frequency. Moreover, the fabrication of a MSM-photodiode
is relatively easy. Another good option would be the use of a
PIN-photodiode. This element also has a low capacitance, but it is
somewhat more difficult to integrate this component in an array.
Another very useful option is an avalanche photodiode.
[0088] As mentioned earlier, the data rate and thus the required
modulation frequency are very large. In order to be able to
modulate at this rate, suitable switching circuitry is important.
Besides the three optical carriers, which will be discussed below,
other related means to transfer modulated light beams are embodied
by the present invention.
Transfer Options
Free Space Optical Interconnects
[0089] When the pattern information carrying light beams are
projected on the corresponding light sensitive elements through the
same medium as wherein the irradiated beamlets are traveling,
several complications arise. It is often not possible to project
the pattern information carrying light beams on the light sensitive
elements perpendicular to the plane wherein the light sensitive
element is located. This can for instance be the case when the
irradiated beamlets are already projected perpendicular to said
plane. The interference between the beamlet and the pattern
information carrying light beam might have an influence on the
pattern, which results in an incorrect data transfer from control
unit towards target exposure surface. To avoid this problem the
pattern information carrying light beams reach the light sensitive
surface of the light sensitive element, say a photodiode, at a
certain angle. However, when this angle of incidence a increases,
the spot size of the pattern information carrying light beams on
the light sensitive surface of the photodiode increases as well. In
order to address each photodiode individually, the spot size of the
pattern information carrying light beams should be less than the
light sensitive surface area or the photodiode. The angle of
incidence .alpha. should therefore be as small as possible.
However, this is not always possible due to obstacles as shown in
FIG. 2A.
[0090] With a smart choice of the location of both fiber array 2
and obstacle 1, some of the problems may be avoided. However, this
is not always possible. The present invention includes ways to
reduce the angle of incidence .alpha. without removal or
replacement of the obstacle 1. A first option is to make the
obstacle 1 transparent for the pattern information carrying light
beams. If the barrier is for instance an electrostatic lens array,
it can for instance be made of some kind of conductive glass or
polymer. Alternatively, the wavelength of the pattern information
carrying light beams can be chosen in such a way that the obstacle
1 becomes transparent for these beams. Silicon, for instance,
becomes transparent for wavelengths larger than 1100 nm. So when a
standard fiber wavelength of 1500 nm is used, the emitted beams
will pass the silicon barrier without noticing its existence.
[0091] Another possibility to reduce the angle of incidence .alpha.
without removing the obstacle 1 is to use more optical fiber arrays
2. In FIG. 2A a situation is sketched wherein the pattern
information carrying light beams leaving the fiber array 2 are
projected on a plate 3 covered with modulators. The emitted beams
cover the total plate 3. If in this configuration the projected
spot size is too large, the angle of incidence can be reduced by
moving the fiber array 2 away from the modulation means plate 3
perpendicular to the plane wherein the photodiodes are deposited as
is shown in FIG. 2B. As a result the critical angle of incidence
.alpha.sub.1 is reduced. Now the spot size may be limited within
the requirements. However, only half of the plate 3 is illuminated.
By using a second fiber array 2 at the same height at the opposite
side of the modulation plate 3 as shown in FIG. 2C, the entire
plate 3 is illuminated and the spot size is small enough. Both
optical fiber arrays 2 comprise halt the amount of fibers compared
to the original one. By selecting the right amount of optical fiber
arrays 2, a plate provided with an array of light sensitive
elements can be illuminated with the desired angle of incidence
.alpha.sub.1.
[0092] FIGS. 3A and 3B show a top view of a squared and a
rectangular modulation plate 3. The dotted lines bound the area
illuminated by one fiber array. As already explained earlier, one
fiber array may not be enough. In that case for instance 2, 4 or 6
optical fiber arrays 2 can be used to illuminate the entire plate
within the requirements.
[0093] Furthermore it is possible to couple the pattern information
carrying light beams into the system via some reflections. The
obstacle 1 can for instance be coated with a reflective material.
Moreover additional mirrors can be placed on strategic positions in
the system to create the desired angle of incidence.
[0094] The pattern information carrying light beam has a diameter
of about 50-150 .mu.m when a multi mode optical fiber is used. A
single mode fiber, on the other hand, only has a diameter of about
1-10 .mu.m. The light sensitive surface of a photodiode can be in
the order of 10-30 microns squared.
[0095] In an embodiment, multi mode optical fibers are used, so the
diameter of the pattern information carrying light beams leaving
the optical fiber array needs to be reduced. Furthermore some kind
of focusing has to be arranged to realize projection with the
correct resolution.
[0096] An optical assembly may be needed to perform both reduction
and focusing of the pattern information carrying light beams. There
are several properties of the light beams that can easily be
modified. The diameter of the light beams leaving the optical fiber
array 2 can be demagnified, and/or the distance between two
adjacent light beams, the so-called pitch, can be reduced by
optical means.
[0097] Focusing light beams leaving the optical fiber array 2 on
the modulation plate 3 can most easily be achieved when both
optical fiber array 2 and modulation array 3 are lying parallel to
each other. If the two planes are not parallel the spot size of
each individual light beam on the modulation array 3 will vary. The
projection of the fiber array 2 on the modulation plate 3 is done
with a lens 5. Often the light beams are projected on the
modulation plate 3 with an angle of incidence unequal to zero. The
optical fibers 4 in the optical fiber array 2 may then be arranged
in such a way that the light beam leaving the optical fiber is
directed towards the lens as is shown in FIG. 4. In this way a
sufficient illumination of the lens s is ensured.
[0098] When the lens 5 is located exactly in the middle between the
optical fiber array 2 and modulation plate 3, 1:1 projection takes
place. Moving the lens towards the modulation plate 3 reduces both
diameter and pitch of the pattern information carrying light beams.
Moving the lens 5 in the other direction, i.e. in the direction of
the optical fiber array 2, will result in an increase of both
parameters.
[0099] For an optimum performance regarding both reduction and
projection more lenses may be needed. A possible configuration with
two lenses 6 and 7 is shown in FIG. 5A. The entire image and
thereby the diameter of each individual pattern information
carrying light beam 8 leaving the optical fiber array 2 is reduced.
In an embodiment with obstacles, mirrors can be used to project the
light beams on the light sensitive elements.
[0100] In some cases the beam diameter needs to be reduced more
than the pitch between the adjacent light beams. In FIG. 5B, an
alternative embodiment is shown. In this embodiment, a micro lens
array 9 positioned between the optical fiber array 2 and a
projection lens 7 can arrange this. Each individual lens of the
micro lens array corresponds to a single fiber 4 in the optical
fiber array 2. The diameter of each pattern information carrying
light beam 8 leaving the optical fiber array 2 is individually
demagnified in this configuration as depicted in FIG. 5B. A
projection lens 7 focuses all the demagnified beams onto the
corresponding light sensitive elements. When direct projection is
impossible due to some obstacle, mirrors can be used to project the
pattern information carrying light beams on the light sensitive
elements at the desired angle of incidence .alpha..
[0101] Another potential problem related to the spot size, cross
talk between adjacent pattern information carrying light beams
emitted from the fiber array 2, can be reduced by applying several
measures. Consider again that the beams are projected on an array
of modulation means wherein the light sensitive surfaces of for
instance photodiodes are all lying within one plane at one side of
the array.
[0102] A solution to this cross talk problem is depicted in FIG.
6A. The area between adjacent light sensitive elements is covered
with a reflective layer 10. The major part of the incoming light
beam falls on the light sensitive converter element 11. The part of
the light beam that is not falling on the element 11 is reflected
back into the system, without affecting any of the adjacent
elements. Coating the light sensitive elements 11 with an
anti-reflective layer can enhance the light detection efficiency
even further.
[0103] Cross talk can also be reduced using a diffusive layer 12 on
top of the entire array 3, as shown in FIG. 6B. The incoming light
is now scattered in all directions. Due to scattering, the light
intensity of the reflected beam drops dramatically.
[0104] Yet another way to reduce the cross talk is to use a filter
located on top of the light sensitive converter element 11.
Examples are a wavelength filter 13 as shown in FIG. 6C, or a
polarization filter. The wavelength filter 13 enhances the
selectivity for a certain wavelength. As a result, waves coming
from adjacent patterned beams with a slightly different wavelength
are filtered out. A filter only transmitting light polarized in a
predetermined direction works has the same effect.
[0105] Yet another possible measure is to make the light sensitive
elements 11 only sensitive for light coming from a predetermined
direction, for instance by incorporating small prisms 14 or
gratings 15 in the modulation array 3 as depicted in FIG. 6D. Only
the light falling on the light sensitive element 11 at the correct
angle and coming from the right direction is used in the modulation
process. Light coming from all other directions is excluded.
Optical Wave-Guides
[0106] A second possibility to transfer the pattern information
carrying light beams leaving the optical fiber array 2 towards the
light sensitive elements 11 embedded in the modulation means is the
use of planar optical wave-guides. Planar optical wave-guides can
be thought of as optical fibers embedded into or onto a substrate.
Consider again the array of modulation means 3. When planar optical
wave-guides are integrated in this array, a system as schematically
shown in FIG. 7 is constructed. Each individual pattern information
carrying light beam 8 leaving the optical fiber array 2 has to be
coupled into the corresponding optical wave-guide 16 directly or
via an array of lenses 17 as shown in FIG. 7. Each lens then
couples an individual pattern information carrying light beam 8
into the entrance point of the corresponding planar optical
wave-guide 16. The optical wave-guide 16 transports the pattern
information carrying light beam 8 through the modulation array 3
towards the correct light sensitive element 11. The light sensitive
element 11 converts the pattern information carrying light beam 8
into a sequence of signals, which activate or deactivate the
modulators 18. Consequently the incoming beamlet will be controlled
according to the pattern information. The sequence of signals in
this embodiment is transported through electric wires 19 embedded
in the modulation array 3 towards the modulators 18.
[0107] FIG. 8 shows a top view of the same configuration as
depicted in FIG. 7. In this case two fiber arrays 2 are used to
control all the modulators 18. However, any number of arrays 2 is
applicable. The light sensitive elements 11 are represented by
squares, the modulators 18 by circles. Only two trajectories of
pattern information carrying light beams 8 are shown for clarity
reasons.
Optical Fibers
[0108] A third possibility for the data transfer from the control
unit towards light sensitive element 11 is to use optical fibers
for the entire trajectory. The major problem with this approach is
the connection of the individual fibers 4 to the structure wherein
the modulation means are integrated. Again imagine that a
modulation array 3 is used. Connecting the individual fibers 4 to
this array 3 may give problems when for instance this array 3 is
moving for scanning purposes. Mechanisms like stress and friction
are introduced in the region of attachment. Eventually the
connection can break. This can be avoided by combining a group of
optical fibers 4 to form a fiber ribbon 20. The ribbon 20 is then
connected at the side of the modulation array 3 as shown in FIG. 9,
showing only two ribbons 20. Another number of ribbons 20 is also
possible. Two exemplary trajectories of optical fibers within the
fiber ribbon are schematically shown with dashed lines. The light
sensitive elements 11, represented in the figure as squares, may be
located close to the contact of the fiber ribbon 20 with the
modulation array 3, but they may also be located closer to the
incoming beamlets. Preferably the optical signals are converted in
electric signals. These signals are transported through on chip
electric wires 19 towards the modulators 19, represented by
circles, located in close proximity of the corresponding incoming
irradiated beamlets. The drawing only shows a number of the
modulators present on the modulation array 3.
EXAMPLES
[0109] The next two sections describe two examples of maskless
lithography systems embodied by the present invention.
Example 1
Maskless Electron Beam Lithography System (FIG. 10)
[0110] In the maskless electron beam lithography system used in
this example, the system comprises an aperture plate comprising
electrostatic deflectors 21 to deflect incoming electron beamlets
22 passing through the apertures 23. This plate will be referred to
as the beamlet blanker array 24. When the electron beamlets 22 have
passed the beamlet blanker array 24 they will reach a second
aperture array (beam stop array) 25 on which their trajectory will
terminate when they are deflected.
[0111] The modulation concept of this lithography system is shown
in FIG. 10. Incoming electron beamlets 22 are projected on the
beamlet blanker array 24. The positions of the electron beamlets 22
correspond to the positions of the apertures 23 in the plate 24.
The beamlet blanker plate 24 comprises a deflector element as
modulation means. In this example said deflector element comprises
an electrostatic deflector 21. Depending on the received
information the deflector 21 located in the beam blanker array 24
will be turned on or off. When the deflector 21 is turned on, an
electric field is established across the aperture 23, which results
in a deflection of the beamlet 22 passing this aperture 23. The
deflected electron beamlet 27 will then be stopped by the beamlet
stop array 25. In this case no information will reach the target
exposure surface When the deflector 21 is turned off the beamlet
will be transmitted. Each transmitted beamlet 28 will be focused on
the target exposure surface. By moving the target exposure surface
and the assembly of arrays relatively to one another and by
scanning the beamlets with for instance an additional beamlet
deflector array a pattern can be written.
[0112] FIG. 11 shows a possible configuration of the usage of free
space interconnects in this maskless lithography system. The
pattern information carrying light beams B coming out of and
leaving the optical fiber array 2 of the optical transmitter are
demagnified by two lenses 29. Alternatively also other
configurations as for instance shown in FIG. 5 can be used. The
pattern information carrying light beams 8 are then projected on
the beamlet blanker plate 24 with a mirror 30 and a focusing lens
7. The angle or incidence .alpha. ranges from 0 and 80 degrees. If
.alpha. is larger than 80 degrees or a smaller angle is desired due
to other complications the beamlet blanker plate 24 can be
illuminated with more than one fiber array 2 as is shown in FIG.
12. In the depicted situation of FIG. 12, 4 fiber arrays 2
illuminate the beamlet blanker plate 24. In FIG. 12 the 4
corresponding focusing lenses 7 are depicted, focusing the pattern
information carrying light beams 8 on the respective part of the
beamlet blanker plate 24.
Example 2
Maskless Optical Lithography System (FIG. 13)
[0113] The maskless lithography system in this example comprises a
spatial light modulator (SLM) 40. Maskless lithography systems
using an SLM are in a general way disclosed in WO 0118606. The SLM
comprises an array of mirrors, which reflect the incoming light
beams in such a way that the beam eventually is blanked or
transmitted. An example of such an SLM is a deformable mirror
device (DMD). A DMD is controlled in the same way as the
electrostatic deflector array shown in the first example. The
modulation signals couple into the system from the back or from the
side.
[0114] One configuration is a backside control of the modulation.
By providing the backside of each mirror with a light sensitive
element, the control can be done with the use of the same optical
carriers as mentioned before. Probably the use of free space
optical interconnects is the most convenient option.
[0115] A schematic drawing of the operation is shown in FIG. 13. A
laser 41 emits a light beam 42, which is split into a plurality of
beamlets 44 by a beam splitter 43. The plurality of beamlets 44 is
projected on the SLM 40. Pattern information carrying light beams
46 sent from the control unit 45 to the SLM 40 control the
transmission probability of beamlets 44 coming from the beam
splitter 43. The transmitted beamlets 47 are focused on the target
exposure surface 49 using lens 48 (which can also be a lens
system).
[0116] By moving the target exposure surface 49 and the rest of the
system relatively to each other a pattern can be written.
[0117] In FIG. 14, an overall side view is shown of a lithography
system in which the modulation means ends 2 of optical fibers are
projected an modulator array 24 using optical system 54,
represented by lenses 54. Modulated light beams 8 from each optical
fiber end are projected on a light sensitive element of a
modulator. In particular, ends of the fibers are projected on the
modulator array. Each light beam 8 holds a part of the pattern data
for controlling one or more modulators.
[0118] FIG. 14 also shows a beam generator 50, which generates a
beam 50. Using an optical system 52, this beam is shaped into a
parallel beam. The parallel beam impinges on beam splitter 53,
resulting in a plurality of substantially parallel beamlets 22,
directed to modulation array 24.
[0119] Using the modulators in the modulation array 24, beamlets 27
are deflected away from the optical axis O of the system and
beamlets 28 pass the modulators undeflected.
[0120] Using a beam stop array 25, the deflected beamlets 27 are
stopped.
[0121] The beamlets 28 passing stop array 25 are deflected at
deflector array 56 in a first writing direction, and the cross
section of each beamlet is reduced using projection lenses 55.
During writing, the target surface 49 moves with respect to the
rest of the system in a second writing direction.
[0122] The lithography system furthermore comprises a control unit
60 comprising data storage 61, a read out unit 62 and data
converter 63. The control unit is located remote from the rest of
the system, for instance outside the inner part of a clean room.
Using optical fibers, modulated light beams holding pattern data
are transmitted to a projector 54 which projects the ends of the
fibers on to the modulation array 24.
[0123] It is to be understood that the above description is
included to illustrate the operation of the preferred embodiments
and is not meant to limit the scope of the invention.
[0124] The scope of the invention is to be limited only by the
following claims. From the above discussion, many variations will
be apparent to one skilled in the art that would yet be encompassed
by the spirit and scope of the present invention.
* * * * *