U.S. patent application number 11/123087 was filed with the patent office on 2005-12-15 for device and method for lithography.
Invention is credited to Beck, Marc, Heidari, Babak.
Application Number | 20050274693 11/123087 |
Document ID | / |
Family ID | 34932984 |
Filed Date | 2005-12-15 |
United States Patent
Application |
20050274693 |
Kind Code |
A1 |
Heidari, Babak ; et
al. |
December 15, 2005 |
Device and method for lithography
Abstract
Apparatus and method for transferring a pattern from a template
(10) having a structured surface to a substrate (12) carrying a
surface layer of a radiation polymerisable fluid (14). The
apparatus comprises a first main part (101) and a second main part
(102) having opposing surfaces (104;105), means for adjusting a
spacing (115) between said main parts, support means (106) for
supporting said template and substrate in mutual parallel
engagement in said spacing with said structured surface facing said
surface layer, a radiation source (110) devised to emit radiation
into said spacing. A cavity (115) has a first wall comprising a
flexible membrane (113) devised to engage said template or
substrate, and means (114;116) are provided for applying an
adjustable overpressure to a medium present in said cavity, whereby
an even distribution of force is obtained over the whole of the
contact surface between the substrate and the template. The
apparatus further includes a heater device having a surface facing
said spacing, for heating either fluid layer (14).
Inventors: |
Heidari, Babak; (Furulund,
SE) ; Beck, Marc; (Hoor, SE) |
Correspondence
Address: |
FINNEGAN, HENDERSON, FARABOW, GARRETT & DUNNER
LLP
901 NEW YORK AVENUE, NW
WASHINGTON
DC
20001-4413
US
|
Family ID: |
34932984 |
Appl. No.: |
11/123087 |
Filed: |
May 6, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60521562 |
May 25, 2004 |
|
|
|
Current U.S.
Class: |
216/52 ; 156/230;
156/345.1; 438/20; 438/586 |
Current CPC
Class: |
B29C 2043/3647 20130101;
B29C 2035/0827 20130101; B29C 43/021 20130101; B29C 35/0888
20130101; B29C 43/10 20130101; B29C 43/003 20130101; B29C 2059/023
20130101; B82Y 40/00 20130101; B29C 59/022 20130101; B82Y 10/00
20130101; G03F 7/0002 20130101; B29C 2043/025 20130101 |
Class at
Publication: |
216/052 ;
156/230; 156/345.1; 438/020; 438/586 |
International
Class: |
G03F 001/00; H01L
021/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 7, 2004 |
EP |
04445057.5 |
Claims
1. Apparatus for transferring a pattern from a template having a
structured surface to a substrate carrying a surface layer of a
radiation polymerisable fluid, said apparatus comprising a first
main part and a second main part having opposing surfaces, means
for adjusting a spacing between said main parts, support means for
supporting said template and substrate in mutual parallel
engagement in said spacing with said structured surface facing said
surface layer, a radiation source devised to emit radiation into
said spacing, a cavity having a first wall comprising a flexible
membrane devised to engage said template or substrate, means for
applying an adjustable overpressure to a medium present in said
cavity, and a heater device having a surface facing said
spacing.
2. The apparatus as recited in claim 1, wherein said radiation
source is positioned in said first main part, devised to emit
radiation into said spacing from a first direction, and said heater
device is positioned in said second main part, having said surface
of the heater device facing said spacing from a second direction,
opposite said first direction.
3. The apparatus as recited in claim 1 or 2, wherein said heater
device comprises a heating element, connected to an energy
source.
4. apparatus as recited in claim 3, wherein said heater device
comprises a cooling element, connected to a cooling source.
5. The apparatus as recited in claim any of the preceding claims,
wherein said medium comprises a gas.
6. The apparatus as recited in claim 5, wherein said medium
comprises air.
7. The apparatus as recited in any of the preceding claims, wherein
said means for applying an adjustable overpressure is arranged to
adjust the pressure to 1-500 bar.
8. The apparatus as recited in any of the preceding claims, wherein
said cavity is defined by a part of the surface of said first main
part, a flexible seal member arranged in and protruding from said
first main part surface, and said membrane which engages said seal
member.
9. The apparatus as recited in claim 8, wherein said membrane is
disconnectable from said seal member, and devised to engage said
seal member by application of pressure from said second main
part.
10. The apparatus as recited in any of the preceding claims,
wherein said membrane is transparent to a wavelength range of said
radiation, said radiation source being positioned behind said
membrane.
11. The apparatus as recited in claim 8, wherein said membrane and
at least a portion of said surface of said first main part is
transparent to a wavelength range of said radiation, said radiation
source being positioned behind said portion of said surface of said
first main part.
12. The apparatus as recited in claim 8, wherein said portion of
said surface of said first main part is made from quartz, calcium
fluoride or any other pressure stable material being transparent to
said radiation.
13. The apparatus as recited in any of the preceding claims,
wherein said radiation source is devised to emit radiation at least
in a wavelength range of 100-500 nm.
14. The apparatus as recited in claim 10, wherein said radiation
source is devised to emit pulsating radiation with a pulse duration
of 0.5-10 .mu.s and a pulse rate of 1-10 pulses per second.
15. The apparatus as recited in any of the preceding claims,
wherein said membrane is made from a polymer material.
16. The apparatus as recited in any of the preceding claims,
wherein said membrane has a diameter or width of 50-1000 mm.
17. The apparatus as recited in any of the preceding claims, where
said substrate acts as said membrane.
18. Method for transferring a pattern from a template having a
structured surface to a substrate carrying a surface layer of a
radiation polymerisable fluid, comprising the steps of: arranging
said template and substrate mutually parallel in an imprint
apparatus, with said structured surface facing said surface layer,
between a stop member and a first side of a flexible membrane;
heating said surface layer by means of a heater device in said
imprint apparatus; applying an overpressure to a medium present on
a second side of the membrane, opposite to said first side, for
imprinting said pattern into said layer; and exposing said layer to
radiation for solidifying said layer.
19. The method as recited in claim 18, further comprising the step
of: baking said layer by providing heat from said heater device
after said step of exposing said layer to radiation.
20. The method as recited in claim 18 or 19, wherein said medium
comprises a gas.
21. The method as recited in claim 20, wherein said medium
comprises air.
22. The method as recited in any of the preceding claims 18-21,
comprising the step of: placing said membrane in direct engagement
with said template or said substrate.
23. The method as recited in claim 18, comprising the step of:
clamping said membrane at a peripheral portion thereof between said
stop member and a seal member, thereby defining a peripheral wall
for a cavity for said medium.
24. The method as recited in claim 18, comprising the steps of:
emitting radiation to said layer through said template, which
template is transparent to a wavelength range of a radiation usable
for polymerising said fluid; and heating said substrate by direct
contact with said heater device.
25. The method as recited in claim 18, comprising the steps of:
emitting radiation to said layer through said substrate, which
substrate is transparent to a wavelength range of a radiation
usable for polymerising said fluid; and heating said template by
direct contact with said heater device.
26. The method as recited in any of the preceding claims 18-25,
comprising the step of: emitting radiation to said layer through
said membrane, which membrane is transparent to a wavelength range
of a radiation usable for polymerising said fluid.
27. The method as recited in any of the preceding claims 18-26,
comprising the step of: emitting radiation to said layer through
said membrane, and through a transparent wall opposing said
membrane, defining a back wall for a cavity for said medium, which
back wall and membrane are transparent to a wavelength range of a
radiation usable for polymerising said fluid.
28. The method as recited in any of the preceding claims 18-27,
wherein the step of exposing said layer comprises the step of:
emitting radiation from a radiation source within a wavelength
range of 100-500 nm.
29. The method as recited in claim 28, comprising the steps of:
emitting pulsating radiation with a pulse duration in the range of
0.5-10 .mu.s and a pulse rate in the range of 1-10 pulses per
second.
30. The method as recited in any of the preceding claims 18-29,
comprising the step of: clamping said substrate and template
together prior to arranging said template and substrate between
said stop member and said flexible membrane.
31. The method as recited in claim 18, comprising the step of:
applying a vacuum between said template and said substrate in order
to extract air inclusions from said surface layer prior to exposing
said layer to radiation.
32. Method for transferring a pattern from a template having a
structured surface to a substrate carrying a surface layer of a
radiation polymerisable fluid, wherein said template includes
protrusions defining a pattern, which protrusions have
non-transparent layers at outer ends, comprising the steps of:
arranging said template and substrate mutually parallel in an
imprint apparatus, with said structured surface facing said surface
layer, between a stop member and a first side of a flexible
membrane; heating said surface layer by means of a heater device in
said imprint apparatus; applying an overpressure to a medium
present on a second side of the membrane, opposite to said first
side, for imprinting said pattern into said layer; and exposing
said layer to radiation for solidifying said layer at portions
between said protrusions.
33. The method as recited in claim 32, further comprising the step
of: baking said layer by providing heat from said heater device
after said step of exposing said layer to radiation.
Description
FIELD OF THE INVENTION
[0001] The invention relates to a device in connection with the
lithography of structures on a micro or nanometre scale. In
particular, the invention relates to imprint lithography on
substrates or objects.
BACKGROUND
[0002] The trend in microelectronics, as well as in micromechanics,
is towards ever smaller dimensions. Some of the most interesting
techniques for fabrication of micro and submicro structures include
different types of lithography.
[0003] Photolithography typically involves the steps of coating a
substrate with a photoresist material to form a resist layer on a
surface of the substrate. The resist layer is then exposed to
radiation at selective portions, preferably by using a mask.
Subsequent developing steps remove portions of the resist, thereby
forming a pattern in the resist corresponding to the mask. The
removal of resist portions exposes the substrate surface, which may
be processed by e.g. etching, doping, or metallisation. For fine
scale replication, photolithography is limited by diffraction,
which is dependent on the wavelength of the radiation used. For
fabrication of structures on a scale of less than 50 nm, such a
short wavelength is needed that the material requirements on the
optical systems will be major.
[0004] An alternative technique is imprint technology. In an
imprint lithography process, a substrate to be patterned is covered
by a mouldable layer. A pattern to be transferred to the substrate
is predefined in three dimensions on a stamp or template. The stamp
is brought into contact with the mouldable layer, and the layer is
softened, preferably by heating. The stamp is then pressed into the
softened layer, thereby making an imprint of the stamp pattern in
the mouldable layer. The layer is cooled down until it hardens to a
satisfactory degree followed by detachment and removal of the
stamp. Subsequent etching may be employed to replicate the stamp
pattern in the substrate. The steps of heating and cooling the
combined stamp and substrate can bring about movement in the
engaging surfaces due to heat expansion. The larger the area to be
imprinted, the larger the actual expansion and contraction, which
can make the imprint process more difficult for larger surface
areas.
[0005] A different form of imprint technology, generally known as
step and flash imprint lithography has been proposed by Willson et
al. in U.S. Pat. No. 6,334,960, and also by Mancini et al in U.S.
Pat. No. 6,387,787. Similar to the imprint technique briefly
described above, this technique involves a template having a
structured surface defining a pattern to be transferred to a
substrate. The substrate is covered by a layer of polymerisable
fluid, into which layer the template is pressed such that the fluid
fills recesses in the pattern structure. The template is made from
a material which is transparent to a radiation wavelength range
which is usable for polymerising the polymerisable fluid, typically
UV light. By applying radiation to the fluid through the template,
the fluid is solidified. The template is subsequently removed,
after which the pattern thereof is replicated in the solid polymer
material layer made from the polymerised fluid. Further processing
transfers the structure in the solid polymer material layer to the
substrate.
[0006] WO 02/067055 to Board of Regents, the University of Texas
System, discloses a system for applying step and flash imprint
lithography. Among other things, this document relates to
production-scale implementation of a step and flash apparatus, also
called a stepper. The template used in such an apparatus has a
rigid body of transparent material, typically quartz. The template
is supported in the stepper by flexure members, which allow the
template to pivot about both X and Y axes, which are mutually
perpendicular in a plane parallel to the substrate surface to be
imprinted. This mechanism also involves a piezo actuator for
controlling parallelism and the gap between the template and the
substrate. Such a system is, however, not capable of handling large
area substrate surfaces in a single imprint step. A step and flash
system offered on the market is the IMPRIO 100, provided by
Molecular Imprints, Inc, 1807-C West Braker Lane, Austin, Tex.
78758, U.S.A. This system has a template image area of 25.times.25
mm, and a street width of 0.1 mm. Although this system is capable
of handling substrate wafers of up to 8 inches, the imprint process
has to be repeated by lifting the template, moving it sideways, and
lowering it to the substrate again, by means of an X-Y translation
stage. Furthermore, for each such step, renewed alignment as well
as new deposition of polymerisable fluid has to be performed. This
technique is therefore very time-consuming, and less than optimum
for large scale production. Furthermore, besides problems of
repeated alignment errors, and high accuracy demands on the
translation stage, this technique suffers from the drawback that
continuous structures which are larger than said template size
cannot be produced. All in all, this means the productions costs
may be too high to make this technique interesting for large scale
production of fine structure devices.
SUMMARY OF THE INVENTION
[0007] Accordingly, an object of the present invention is to
provide methods and means for improving fabrication of structures
comprising three-dimensional features on a micro or nanometre
scale. In particular, it is an object to provide improved methods
and means for transferring a pattern of such structures to
substrates having widths of more than one inch, and even for 8 inch
diameters, 12 inch diameters, and larger. An aspect of this object
is to provide an apparatus and an associated process which is more
cost effective and more versatile.
[0008] According to a first aspect, this object is fulfilled by an
apparatus for transferring a pattern from a template having a
structured surface to a substrate carrying a surface layer of a
radiation polymerisable fluid, said apparatus comprising a first
main part and a second main part having opposing surfaces, means
for adjusting a spacing between said main parts, support means for
supporting said template and substrate in mutual parallel
engagement in said spacing with said structured surface facing said
surface layer, a radiation source devised to emit radiation into
said spacing, a cavity having a first wall comprising a flexible
membrane devised to engage said template or substrate, means for
applying an adjustable overpressure to a medium present in said
cavity, and a heater device having a surface facing said spacing.
Due to the flexible membrane, an absolutely even distribution of
force is obtained over the whole of the contact surface between the
substrate and the template, whereby patterning of large area
substrates in a single imprint step is made possible.
[0009] Preferably, said radiation source is positioned in said
first main part, devised to emit radiation into said spacing from a
first direction, and said heater device is positioned in said
second main part, having said surface of the heater device facing
said spacing from a second direction, opposite said first
direction.
[0010] In one embodiment, said heater device comprises a heating
element, connected to an energy source.
[0011] In one embodiment, said heater device comprises a cooling
element, connected to a cooling source.
[0012] Preferably, said medium comprises a gas or a liquid.
[0013] In one embodiment, said medium comprises air.
[0014] In one embodiment, said means for applying an adjustable
overpressure is arranged to adjust the pressure to 1-500 bar.
[0015] Preferably, said cavity is defined by a part of the surface
of said first main part, a flexible seal member arranged in and
protruding from said first main part surface, and said membrane
which engages said seal member.
[0016] In a preferred embodiment, said membrane is disconnectable
from said seal member, and devised to engage said seal member by
application of pressure from said second main part.
[0017] Preferably, said membrane is transparent to a wavelength
range of said radiation, said radiation source being positioned
behind said membrane.
[0018] In one embodiment, said membrane and at least a portion of
said surface of said first main part is transparent to a wavelength
range of said radiation, said radiation source being positioned
behind said portion of said surface of said first main part.
[0019] In a preferred embodiment, said portion of said surface of
said first main part is made from quartz, calcium fluoride or any
other pressure stable material being transparent to said
radiation.
[0020] Preferably, said radiation source is devised to emit
radiation at least in a wavelength range of 100-500 nm.
[0021] In a preferred embodiment, said radiation source is
air-cooled and devised to emit pulsating radiation with a pulse
duration of 0.5-10 .mu.s and a pulse rate of 1-10 pulses per
second.
[0022] In one embodiment, said membrane consists of a polymer
material.
[0023] In a preferred embodiment, said membrane has a diameter or
width of 50-1000 mm.
[0024] In one embodiment, said substrate acts as said membrane.
[0025] According to a second aspect, the object of the present
invention is fulfilled by a method for transferring a pattern from
a template having a structured surface to a substrate carrying a
surface layer of a radiation polymerisable fluid, comprising the
steps of:
[0026] arranging said template and substrate mutually parallel in
an imprint apparatus, with said structured surface facing said
surface layer, between a stop member and a first side of a flexible
membrane;
[0027] heating said surface layer by means of a heater device in
said imprint apparatus;
[0028] applying an overpressure to a medium present on a second
side of the membrane, opposite to said first side, for imprinting
said pattern into said layer; and
[0029] exposing said layer to radiation for solidifying said
layer.
[0030] In a preferred embodiment, the method further comprises the
step of:
[0031] baking said layer by providing heat from said heater device
after said step of exposing said layer to radiation.
[0032] Preferably, said medium comprises a gas or a liquid.
[0033] In one embodiment, said medium comprises air.
[0034] Preferably, the method comprises the step of:
[0035] placing said membrane in direct engagement with said
template or said substrate.
[0036] In a preferred embodiment, the method comprises the step
of:
[0037] clamping said membrane at a peripheral portion thereof
between said stop member and a seal member, thereby defining a
peripheral wall for a cavity for said medium.
[0038] Preferably, the method comprises the steps of:
[0039] emitting radiation to said layer through said template,
which template is transparent to a wavelength range of a radiation
usable for polymerising said fluid; and
[0040] heating said substrate by direct contact with said heater
device.
[0041] Alternatively, the method may comprise the steps of:
[0042] emitting radiation to said layer through said substrate,
which substrate is transparent to a wavelength range of a radiation
usable for polymerising said fluid; and
[0043] heating said template by direct contact with said heater
device.
[0044] In a preferred embodiment, the method comprises the step
of:
[0045] emitting radiation to said layer through said membrane,
which membrane is transparent to a wavelength range of a radiation
usable for polymerising said fluid.
[0046] Preferably, the method comprises the step of:
[0047] emitting radiation to said layer through said membrane, and
through a transparent wall opposing said membrane, defining a back
wall for a cavity for said medium, which back wall and membrane are
transparent to a wavelength range of a radiation usable for
polymerising said fluid.
[0048] In one embodiment, the step of exposing said layer comprises
the step of:
[0049] emitting radiation from a radiation source within a
wavelength range of 100-500 nm.
[0050] In a preferred embodiment, the method comprises the steps
of:
[0051] air-cooling said radiation source, and emitting pulsating
radiation with a pulse duration in the range of 0.5-10 .mu.s and a
pulse rate in the range of 1-10 pulses per second.
[0052] In one embodiment, the method comprises the step of:
[0053] using said substrate as said membrane.
[0054] In another embodiment, the method comprises the step of:
[0055] clamping said substrate and template together prior to
arranging said template and substrate between said stop member and
said flexible membrane.
[0056] In yet another embodiment, the method comprises the step
of:
[0057] applying a vacuum between said template and said substrate
in order to extract air inclusions from said surface layer prior to
exposing said layer to radiation.
[0058] According to a third aspect, the object of the present
invention is fulfilled by a method for transferring a pattern from
a template having a structured surface to a substrate carrying a
surface layer of a radiation polymerisable fluid, wherein said
template includes protrusions defining a pattern, which protrusions
have non-transparent layers at outer ends, comprising the steps
of:
[0059] arranging said template and substrate mutually parallel in
an imprint apparatus, with said structured surface facing said
surface layer, between a stop member and a first side of a flexible
membrane;
[0060] heating said surface layer by means of a heater device in
said imprint apparatus;
[0061] applying an overpressure to a medium present on a second
side of the membrane, opposite to said first side, for imprinting
said pattern into said layer; and
[0062] exposing said layer to radiation for solidifying said layer
at portions between said protrusions.
[0063] In a preferred embodiment, the method further comprises the
step of:
[0064] baking said layer by providing heat from said heater device
after said step of exposing said layer to radiation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0065] The invention will be described in greater detail below with
reference to the accompanying drawings, on which:
[0066] FIGS. 1-3 schematically illustrate the main process steps
for transferring a pattern from a template to a substrate, wherein
radiation is applied through a transparent template to solidify a
polymerisable fluid on the substrate surface;
[0067] FIGS. 4-6 schematically illustrate corresponding process
steps for transferring a pattern from a template to a substrate,
wherein radiation is applied through a transparent substrate to
solidify a polymerisable fluid on the substrate surface;
[0068] FIG. 7 schematically illustrates an embodiment of an
apparatus according to the invention, for performing the process as
generally described in FIGS. 1-3 or 4-6;
[0069] FIG. 8 schematically illustrates the apparatus of FIG. 7,
when loaded with a template and a substrate at an initial step of
the process;
[0070] FIG. 9 illustrates the apparatus of FIGS. 7 and 8, at an
active process step of transferring a pattern from the template to
the substrate; and
[0071] FIGS. 10-12 illustrates an alternative embodiment of an
imprint process according to the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0072] The present invention relates, in general, to a method of
transferring a pattern from a template to a substrate, by creating
a relief image of a structure on a surface of the template on a
surface of the substrate. The surface of the template and the
surface of the substrate are in this process arranged generally
parallel to each other, and the transfer of the pattern is obtained
by pressing the structured template surface into a formable layer
disposed on the substrate surface. The formable layer is treated to
solidify, such that its shape is forced to resemble the template
surface. The template can thereafter be removed from the substrate
and its layer, said layer now being an inverted topographical
replica of the template. In order to permanent the transferred
pattern in the substrate, further processing may be required.
Typically, wet or dry etching is performed to selectively etch the
surface of the substrate under the solidified layer, whereby the
pattern in the solidified layer is transferred to the substrate
surface. This much is state of the art, and is well described in
prior art documents, such as the aforementioned U.S. Pat. No.
6,334,960.
[0073] FIGS. 1-3 schematically present the basic process steps of
the actual pattern transfer steps, or imprint steps, of an
embodiment of the invention.
[0074] In FIG. 1 a template 10 is illustrated, the template having
a structured surface 11, in which three-dimensional protrusions and
recesses are formed with a feature size in height and width within
a range of 1 nm to several .mu.m, and potentially both smaller and
larger. The thickness of template 10 is typically between 10 and
1000 .mu.m. A substrate 12 has a surface 17 which is arranged
substantially parallel to template surface 11, with an intermediate
spacing between the surfaces at the initial stage shown in FIG. 1.
The substrate 12 comprises a substrate base 13, to which the
pattern of template surface 11 is to be transferred. Though not
shown, the substrate may also include a support layer below the
substrate base 13. In a process where the pattern of template 10 is
to be transferred to substrate 12 directly through an imprint in a
polymerisable fluid, said fluid may be applied as a surface layer
14 directly onto the substrate base surface 17. In alternative
embodiments, indicated by the dashed line, a transfer layer 15 is
also employed, of e.g. a polymer. Examples of such, and how they
are used in the subsequent process of transferring the imprinted
pattern to the substrate base 13, are also described in U.S. Pat.
No. 6,334,960. In an embodiment including a transfer layer 15,
substrate surface 17 denotes the upper or outer surface of the
transfer layer 15, which in turn is arranged on the substrate base
surface 18.
[0075] Substrate 12 is positioned on a heater device 20. Heater
device 20 preferably comprises a heater body 21 of metal, e.g.
aluminium. A heater element 22 is connected to or included in
heater body 21, for transferring thermal energy to heater body 21.
In one embodiment, heater element 22 is an electrical immersion
heater inserted in a socket in heater body 21. In another
embodiment, an electrical heating coil is provided inside heater
body 21, or attached to a lower surface of heater body 21. In yet
another embodiment, heating element 22 is a formed channel in
heater body 21, for passing a heating fluid through said channel.
Heater element 22 is further provided with connectors 23 for
connection to an external energy source (not shown). In the case of
electrical heating, connectors 23 are preferably galvanic contacts
for connection to a current source. For an embodiment with formed
channels for passing a heating fluid, said connectors 23 are
preferably conduits for attachment to a heated fluid source. The
heating fluid may e.g. be water, or an oil.
[0076] Heater body 21 is preferably a piece of cast metal, such as
aluminium, stainless steel, or other metal. Furthermore, a body 21
of a certain mass and thickness is preferably used such that an
even distribution of heat at an upper side of heater device 20 is
achieved, which upper side is connected to substrate 12 for
transferring heat from body 21 through substrate 12 to heat layer
14. For an imprint process used to imprint 2.5" substrates, a
heater body 21 of at least 2.5" diameter, and preferably 3" or
more, is used, with a thickness of at least 1 cm, preferably at
least 2 or 3 cm. For an imprint process used to imprint 6"
substrates, a heater body 21 of at least 6" diameter, and
preferably 7" or more, is used, with a thickness of at least 2 cm,
preferably at least 3 or 4 cm. Heater device 20 is preferably
capable of heating heater body 21 to a temperature of
200-300.degree. C., though lower temperatures will be sufficient
for most processes.
[0077] For the purpose of providing controlled cooling of layer 14,
heater device 20 is further provided with a cooling element 24
connected to or included in heater body 21, for transferring
thermal energy from heater body 21. In a preferred embodiment,
cooling element 24 comprises a formed channel or channels in heater
body 21, for passing a cooling fluid through said channel or
channels. Cooling element 24 is further provided with connectors 25
for connection to an external cooling source (not shown).
Preferably, said connectors 25 are conduits for attachment to a
cooling fluid source. Said cooling fluid is preferably water, but
may alternatively be an oil, e.g. an insulating oil, or any other
suitable coolant.
[0078] Examples of available and usable polymerisable or curable
fluids for layer 14 comprise NIP-K17 and NIP-K22 from ZEN
Photonics, 104-11 Moonj i-Dong, Yusong-Gu, Daejeon 305-308, South
Korea. NIP-K17 has a main component of acrylate, and has a
viscosity at 25.degree. C. of about 9.63 cps. NIP-K22 also has a
main component of acrylate, and a viscosity at 25.degree. C. of
about 5.85 cps. Both substances are devised to cure under exposure
to ultraviolet radiation above 12 mW/cm.sup.2 for 2 minutes.
[0079] Another example of an available and usable polymerisable
fluid for layer 14 is Ormocore from Micro Resist Technology GmbH,
Koepenicker Strasse 325, Haus 211, D-12555 Berlin, Germany. This
substance has a composition of inorganic-organic hybrid polymer,
unsaturated, with a 1-3% photopolymerisation initiator. Viscosity
is 3-8 mPas at 25.degree. C., and the fluid may be cured under
exposure of radiation with 500 mJ/cm.sup.2 at a wavelength of 365
nm. Other examples of polymerisable materials are mentioned in U.S.
Pat. No. 6,334,960.
[0080] The thickness of layer 14 when deposited on the substrate
surface is typically 10 nm-10 .mu.m, depending on application area.
The polymerisable fluid may be applied by spin coating, roller
coating, dip coating or similar. A typical advantage with the
present invention, compared to the prior art step and flash method,
is that the polymer fluid may be spin coated on the entire
substrate, which is an advantageous and fast process. The step and
flash method, on the other hand, has to use repeated dispensation
by dripping on repeated surface portions, since that method is
incapable of handling large surfaces in single steps.
[0081] The arrows of FIG. 1 illustrate that the template surface 11
is pressed into surface 16 of the polymerisable fluid layer 14. At
this step, heater device 20 is preferably used to control the
temperature of layer 14, for obtaining a suitable viscosity in the
material of layer 14.
[0082] FIG. 2 illustrates how the structures of template surface 11
has made an imprint in the fluid layer 14, at which the fluid has
been forced to fill the recesses in template surface 11. In the
illustrated embodiment, the highest protrusions in template surface
11 do not penetrate all the way down to substrate surface 17. This
may be beneficial for protecting the substrate surface 17, and
particularly the template surface 11, from damage. However, in
alternative embodiments, such as one including a transfer layer,
imprint may be performed all the way down to transfer layer surface
17. In the embodiment illustrated in FIGS. 1-3, the template is
made from a material which is transparent to radiation 19 of a
predetermined wavelength or wavelength range, which is usable for
solidifying a selected polymerisable fluid. Such materials may e.g.
be quartz or various forms of polymers, dependent on the radiation
wavelength. Radiation 19 is typically applied when template 10 has
been pressed into fluid layer 14 with a suitable alignment between
template 10 and substrate 12. When exposed to this radiation 19,
solidification of the polymerisable fluid is initiated, for
solidification to a solid body 14' taking the shape determined by
the template 10. However, heater device 20 is preferably used to
provide heat to layer 14', for baking layer 14' to a solid body
before separation of template 10 and substrate 12.
[0083] The template 10 is thereafter removed, e.g. by a peeling and
pulling process. The formed and solidified polymer layer 14'
remains on the substrate 12. The various different ways of further
processing of the substrate and its layer 14' will not be dealt
with here in any detail, since the invention as such is neither
related to such further processing, nor is it dependent on how such
further processing is achieved.
[0084] FIGS. 4-6 schematically present the basic process steps of
the actual pattern transfer steps, or imprint steps, of an
alternative embodiment of the invention. The only real difference
from the embodiment of FIGS. 1-3 is that in this embodiment the
radiation 19 is applied through substrate 12 instead of through
template 10, while the same reference marks have been used.
Furthermore, heater device 20 is instead connected to template 10,
for heating layer 14 through template 10. Heater device 20 of FIGS.
4-6 otherwise comprises the same features as the heater device of
FIGS. 1-3, wherefore the same reference markings have been used. No
further explanation of the features of FIGS. 4-6 will therefore be
made.
[0085] FIG. 7 schematically illustrates a preferred embodiment of
an apparatus according to the present invention, also usable for
carrying out an embodiment of the method according to the present
invention. It should be noted that this drawing is purely
schematic, for the purpose of clarifying the different features
thereof. In particular, dimensions of the different features are
not on a common scale.
[0086] The apparatus 100 comprises a first main part 101 and a
second main part 102. In the illustrated preferred embodiment these
main parts are arranged with the first main part 101 on top of
second main part, with an adjustable spacing 103 between said main
parts. When making a surface imprint by a process as illustrated in
FIGS. 1-6, it may be of great importance that the template and the
substrate are properly aligned in the lateral direction, typically
called the X-Y plane. This is particularly important if the imprint
is to be made on top of or adjacent to a previously existing
pattern in the substrate. However, the specific problems of
alignment, and different ways of overcoming them, are not addressed
herein, but may of course be combined with the present invention
when needed.
[0087] The first, upper, main part 101 has a downwards facing
surface 104, and the second, lower, main part 102 has an upwards
facing surface 105. Upwards facing surface 105 is, or has a portion
that is, substantially flat, and which is placed on or forms part
of a plate 106 which acts as a support structure for a template or
a substrate to be used in an imprint process, as will be more
thoroughly described in conjunction with FIGS. 8 and 9. A heater
body 21 is placed on plate 106, or forms part of plate 106. Heater
body 21 forms part of a heater device 20, and includes a heating
element 22 and preferably also a cooling element 24, as shown in
FIGS. 1-6. Heating element 22 is connected through connectors 23 to
a energy source 26, e.g. an electrical power supply with current
control means. Furthermore, cooling element 24 is connected through
connectors 25 to a cooling source 27, e.g. a cooling fluid
reservoir and pump, with control means for controlling flow and
temperature of the cooling fluid.
[0088] Means for adjusting spacing 103 are, in the illustrated
embodiment, provided by a piston member 107 attached at its outer
end to plate 106. Piston member 107 is displaceably linked to a
cylinder member 108, which preferably is held in fixed relation to
first main part 101. As is indicated by the arrow in the drawing,
the means for adjusting spacing 103 are devised to displace second
main part 102 closer to or farther from first main part 101, by
means of a movement substantially perpendicular to the
substantially flat surface 105, i.e. in the Z direction.
Displacement may be achieved manually, but is preferably assisted
by employing either a hydraulic or pneumatic arrangement. The
illustrated embodiment may be varied in a number of ways in this
respect, for instance by instead attaching plate 106 to a cylinder
member about a fixed piston member. It should further be noted that
the displacement of second main part 102 is mainly employed for
loading and unloading the apparatus 100 with a template and a
substrate, and for arranging the apparatus in an initial operation
position. The movement of second main part 102 is, however,
preferably not included in the actual imprint process as such in
the illustrated embodiment, as will be described.
[0089] First main part 101 comprises a peripheral seal member 108,
which encircles surface 104. Preferably, seal member 108 is an
endless seal such as an o-ring, but may alternatively be composed
of several interconnected seal members which together form a
continuous seal 108. Seal member 108 is disposed in a recess 109
outwardly of surface 104, and is preferably detachable from said
recess. The apparatus further comprises a radiation source 110, in
the illustrated embodiment disposed in the first main part 101
behind surface 104. Radiation source 110 is connectable to a
radiation source driver 111, which preferably comprises or is
connected to a power source (not shown). Radiation source driver
111 may be included in the apparatus 100, or be an external
connectable member. A surface portion 112 of surface 104, disposed
adjacent to radiation source 110, is formed in a material which is
transparent to radiation of a certain wavelength or wavelength
range of radiation source 110. This way, radiation emitted from
radiation source 110 is transmitted towards spacing 103 between
first main part 101 and second main part 102, through said surface
portion 112. Surface portion 112, acting as a window, may be formed
in available fused silica, quartz, or glass used for CD/DVD
mastering.
[0090] In operation, apparatus 100 is further provided with a
flexible membrane 113, which is substantially flat and engages seal
member 108. In a preferred embodiment, seal member 113 is a
separate member from seal member 108, and is only engaged with seal
member 108 by applying a counter pressure from surface 105 of plate
106, as will be explained. However, in an alternative embodiment,
membrane 113 is attached to seal member 108, e.g. by means of a
cement, or by being an integral part of seal member 108.
Furthermore, in such an alternative embodiment, membrane 113 may be
firmly attached to main part 101, whereas seal 108 is disposed
outwardly of membrane 113. For an embodiment such as the one
illustrated, also membrane 113 is formed in a material which is
transparent to radiation of a certain wavelength or wavelength
range of radiation source 110. This way, radiation emitted from
radiation source 110 is transmitted into spacing 103 through said
cavity 115 and its boundary walls 104 and 113. Examples of usable
materials for membrane 113, for the embodiment of FIGS. 7-9,
include polycarbonate, polypropylene, polyethylene. The thickness
of membrane 113 may typically be 10-500 .mu.m.
[0091] A conduit 114 is formed in first main part 101 for allowing
a fluid medium to pass to a space defined by surface 104, seal
member 108 and membrane 113, which space acts as a cavity 115 for
said fluid medium. Conduit 114 is connectable to a pressure source
116, such as a pump, which may be an external or a built in part of
apparatus 100. Pressure source 116 is devised to apply an
adjustable pressure, in particular an overpressure, to a fluid
medium contained in said cavity 115. An embodiment such as the one
illustrated is suitable for use with a gaseous pressure medium.
Preferably, said medium is selected from the group containing air,
nitrogen, and argon. If instead a liquid medium is used, it is
preferred to have the membrane attached to seal member 108. Such a
liquid may be a hydraulic oil.
[0092] FIG. 8 illustrates the apparatus embodiment of FIG. 7, when
being loaded with a substrate and a template for a lithographic
process. For better understanding of this drawing, reference is
also made to FIGS. 1-3. Second main part 102 has been displaced
downwards from first main part 101, for opening up spacing 103. As
indicated in FIGS. 1-6, either the template or the substrate are
transparent to radiation of a certain wavelength or wavelength
range of radiation source 110. The illustrated embodiment of FIG. 8
shows an apparatus loaded with a transparent template 10 on top of
a substrate 12. Substrate 12 is placed with a backside thereof on
surface 105 of heater body 21, placed on or in the second main part
102. Thereby, substrate 12 has its substrate surface 17 with the
layer 14 of polymerisable fluid facing upwards. For the sake of
simplicity, all features of heater device 20, as seen in FIGS. 1-6
are not shown in FIG. 8. Template 10 is placed on or adjacent to
substrate 12, with its structured surface 11 facing substrate 12.
Means for aligning template 10 with substrate 12 may be provided,
but are not illustrated in this schematic drawing. Membrane 113 is
then placed on top of template 10. For an embodiment where membrane
113 is attached to the first main part, the step of actually
placing membrane 113 on the template is, of course, dispensed with.
In FIG. 8 template 10, substrate 12 and membrane 113 are shown
completely separated for the sake of clarity only, whereas in a
real situation they would be stacked on surface 105.
[0093] FIG. 9 illustrates an operative position of apparatus 100.
Second main part 102 has been raised to a position where membrane
113 is clamped between seal member 108 and surface 105. In reality,
both template 10 and substrate 12 are very thin, typically only
parts of a millimetre, and the actual bending of membrane 113 as
illustrated is minimal. Still, surface 105 may optionally be
devised with a raised peripheral portion at the point where it
contacts seal member 108 through membrane 113, for compensating for
the combined thickness of template 10 and substrate 12.
[0094] Once main parts 101 and 102 are engaged to clamp membrane
113, cavity 115 is sealed. Pressure source 116 is then devised to
apply an overpressure to a fluid medium in cavity 115. The pressure
in cavity 115 is transferred by membrane 113 to template 10, which
is pressed towards substrate 12 for imprinting the template pattern
in the polymerisable fluid layer 14, cf. FIG. 2. For a polymer
material of layer 14 having sufficient viscosity at the operating
temperature, typically room temperature between 20 and 25.degree.
C., imprint may be made directly. However, certain types of
polymers need pre-heating to overcome its glass transition
temperature TG, which may be about 60.degree. C. An example of such
a polymer is MRL 6000 by Micro Resist Technology. When using such
polymers, the apparatus 100, having combined radiation and heating
capabilities, is particularly useful. Heater device 20 is activated
to heat polymer layer 14 through substrate 12, by means of heater
body 21, until TG has been over come. The pressure of the medium in
cavity 115 is then increased to 5-500 bar, advantageously to 5-200
bar, and preferably to 5-100 bar. Template 10 and substrate 12 are
thereby being pressed together with a corresponding pressure.
Thanks to flexible membrane 113, an absolutely even distribution of
force is obtained over the whole of the contact surface between the
substrate and the template. The template and the substrate are
thereby made to arrange themselves absolutely parallel in relation
to one another and, the influence of any irregularities in the
surface of the substrate or template being eliminated.
[0095] When template 10 and substrate 12 have been brought together
by means of the applied fluid medium pressure, radiation source is
triggered to emit radiation 19. The radiation is transmitted
through surface portion 112, which acts as a window, through cavity
115, membrane 113, and template 10. The radiation is partly or
completely absorbed in the layer 14 of polymerisable fluid, which
thereby is solidified in the perfectly parallel arrangement between
template 10 and substrate 12, provided by the pressure and membrane
assisted compression. Radiation exposure time is dependent on the
type and amount of fluid in layer 14, the radiation wavelength
combined with the type of fluid, and of the radiation power. The
feature of solidifying such a polymerisable fluid is well known as
such, and the relevant combinations of the mentioned parameters are
likewise known to the skilled person. Once the fluid has solidified
to form a layer 14', further exposure has no major effect. However,
dependent on the type of polymerisable fluid, post-baking at an
elevated temperature of 150-160.degree. C. may be necessitated for
a time period of 0.5-1 hour. With the apparatus 100 according to
the present invention, post-baking may be performed in the imprint
machine 100, which means that it is not necessary to bring the
substrate out of the apparatus and into a separate oven. This saves
one process step, which makes both time and cost savings possible
in the imprint process. For the example of MRL 6000, post-baking is
typically performed at 100-120.degree. C. for about 10 minutes. By
performing the post-baking step while the template 10 is still held
with the selected pressure towards substrate 10, higher accuracy in
the resulting structure pattern in layer 14 may also be achieved,
which makes it possible to produce finer structures. Following an
exposure time and possibly post-baking under compression, depending
on the choice of material and radiation, and dimensions of the
polymerisable layer, the pressure in cavity 115 is reduced and the
two main parts 101 and 102 are separated from one another. In one
embodiment, cooling element 24 of heater device 20 may first be
used to cool down the substrate 12 and template 10 before
separation. Substrate 12 and template 10 are thereafter separated
from one another. After this, the substrate is subjected to further
treatment according to what is previously known for imprint
lithography.
[0096] FIGS. 8 and 9 illustrate a process similar to that of FIGS.
1-3. Again, it should be noted that with a transparent substrate
12, template 10 may instead be placed on surface 105 of heater body
21, with substrate on top of template 10, as shown in FIGS.
4-6.
[0097] FIGS. 10-12 illustrates an alternative method of using
apparatus 100, in accordance with an embodiment of the invention.
The same reference markings are used for like features as in FIGS.
1-3. However, in the process of FIGS. 10-12, a transparent template
200 is used, preferably made from glass or quartz. Template 200 has
a structured surface facing substrate 12, with projecting
pattern-defining protrusions 201 having opaque layers 202 covering
the outer end surfaces of protrusions 201. Preferably, layers 202
are metal layers. In a preferred embodiment, template 200 is
manufactured by means of first applying a metal mask 202 on
selected areas of the template surface, where after an etching
process is used for defining grooves between the masked portions.
Instead of removing the mask after the etching step, the mask 202
is kept on the template to define the non-transparent outer end
surfaces of the template protrusions 201. By manufacturing template
200 by means of this process, it is also ensured that a near
completely even common plane for the outer end surfaces of
protrusions 201 is achieved, since the template manufacturing
process starts from a flat template body with a plane surface. It
should be noted that dimensions illustrated in FIGS. 1-12 are
exaggerated for the sake of easy understanding. For instance,
layers 202 may be only a few atomic monolayers thick.
[0098] In FIG. 10, template 200 is pressed into layer 214 on
substrate 12, preferably by using an apparatus as described with
reference to FIGS. 7-9. Layer 214 is in this case a Uv-curable
negative resist polymer, which may be of any known type. An even
pressure is achieved over the entire engaging surfaces of template
200 and substrate 12, thanks to the imprint technique using a
membrane and gas pressure as described above. Preferably, the
template 200 is pressed into layer 214 such that the outer ends of
protrusions 201 come extremely close to substrate layer 17,
preferably only a few nanometres. In one embodiment, heater device
20 is used for pre-heating layer 214 trough substrate 12, in order
for the polymer of layer 214 to overcome the glass transition
temperature.
[0099] In FIG. 11, radiation 19 is applied through template 200,
towards substrate 12. Radiation which hits layers 202 is stopped
and reflected, and does not reach layer portions 214'. Radiation
which radiates between protrusions 201, however, will hit layer 214
and start a curing or solidification process in layer portions
214". Preferably, baking process is then performed using heater
device 20 for completing the curing process.
[0100] In the step illustrated in FIG. 12, template 200 is
separated and removed from template 12, leaving layer 214 as
imprinted. In this shape, substrate 12 is exposed to a negative
resist developer fluid. The exact type of fluid may be of any known
kind, although the skilled person realises that developer type has
to be selected dependent on the resist polymer used. The developer
will only remove portions 214' which were not exposed to radiation,
and which remain only as very thin layers at the bottom of the
recesses in the polymer layer formed by protrusions 201. Compared
to prior art processes, where an ashing or etching process has to
be applied to remove the remaining polymer portions 214' in the
recesses, which is then also cured, this process is considerably
easier and faster. Furthermore, ashing or etching of the patterned
polymer layer 14 will remove material from all parts of layer 214,
both portions 214' and 214", whereas the proposed method only takes
away the portions 214' which were not exposed to radiation.
[0101] One embodiment of the system according to the invention
further comprises mechanical clamping means, for clamping together
substrate 12 and template 10. This is particularly preferred in an
embodiment with an external alignment system for aligning substrate
and template prior to pattern transfer, where the aligned stack
comprising the template and the substrate has to be transferred
into the imprint apparatus. The system may also contain means for
applying a vacuum between template and substrate in order to
extract air inclusions from the polymerisable layer of the stacked
sandwich prior to hardening of the polymerisable fluid through UV
irradiation.
[0102] In a preferred embodiment, the template surface 11 is
preferably treated with an anti-adhesion layer to prevent the cured
polymer layer 14' from sticking to it after the imprint process. An
example of such an anti-adhesion layer comprises a
fluorine-containing group, as presented in WO 03/005124 and
invented by one of the inventors of the instant invention. The
contents of WO 03/005124 are also hereby incorporated by
reference.
[0103] A first mode of the invention, with a transparent template,
which has been successfully tested by the inventors, involves a
substrate 12 of silicon covered by a layer 14 of NIP-K17 with a
thickness of 1 .mu.m. A template of glass or fused silica/quartz,
with a thickness of 600 .mu.m, has been used.
[0104] A second mode of the invention, with a transparent
substrate, which has been successfully tested by the inventors,
involves a substrate 12 of glass or fused silica/quartz covered by
a layer 14 of NIP-K17 with a thickness of 1 .mu.m. A template of
e.g. nickel or silicon has been used, with a thickness of about 600
.mu.m, though any other suitable non-transparent material can be
used.
[0105] After compression by means of membrane 113 with a pressure
of 5-100 bar for about 30 seconds, radiation source 110 is turned
on. Radiation source 110 is typically devised to emit at least in
the ultraviolet region below 400 nm. In a preferred embodiment, an
air-cooled xenon lamp with an emission spectrum ranging from
200-1000 nm is employed as the radiation source 110. The preferred
xenon type radiation source 110 provides a radiation of 1-10
W/cm.sup.2, and is devised to flash 1-5 .mu.s pulses, with a pulse
rate of 1-5 pulses per second. In an alternative embodiment, a
continuous mode UV source is used. A window 112 of quartz is formed
in surface 104 for passing through radiation. Exposure time is
preferably between 1-30 seconds, for polymerising fluid layer 14
into a solid layer 14'. After successful exposure, second main part
102 is lowered to a position similar to that of FIG. 8, following
which template 10 and substrate 12 are removed from the apparatus
for separation and further processing of the substrate.
[0106] The disclosed apparatus and method is particularly
advantageous for large area imprint in a single step, and has as
such huge benefits over the previously known step and flash method.
Thanks to the membrane-transferred fluid pressure, the present
invention can be used for one step imprint of substrates of 8 inch,
12 inch, and even larger discs. Even full flat panel displays with
sizes of about 400.times.600 mm and larger can be patterned with a
single imprint and exposure step with the present invention. The
present invention therefore provides a technique which may for the
first time make radiation-assisted polymerisation imprint
attractive to large scale production. The invention is usable for
forming patterns in a substrate for production of e.g. printed wire
boards or circuit boards, electronic circuits, miniaturised
mechanical or electromechanical structures, magnetic and optical
storage media etc. The apparatus according to the invention may of
course also be used only with the radiation source, or instead only
with the heater device.
[0107] The invention is defined by the appended claims.
* * * * *