U.S. patent application number 10/445578 was filed with the patent office on 2004-02-26 for methods and apparatus of field-induced pressure imprint lithography.
This patent application is currently assigned to PRINCETON UNIVERSITY. Invention is credited to Chou, Stephen Y., Zhang, Wei.
Application Number | 20040036201 10/445578 |
Document ID | / |
Family ID | 46299322 |
Filed Date | 2004-02-26 |
United States Patent
Application |
20040036201 |
Kind Code |
A1 |
Chou, Stephen Y. ; et
al. |
February 26, 2004 |
Methods and apparatus of field-induced pressure imprint
lithography
Abstract
An improved method of imprint lithography involves using
fluid-induced pressure from electric or magnetic fields to press a
mold onto a substrate having a moldable surface. In essence, the
method comprises the steps of providing a substrate having a
moldable surface, providing a mold having a molding surface and
pressing the molding surface and the moldable surface together by
electric or magnetic fields to imprint the molding surface onto the
moldable surface. The molding surface advantageously comprises a
plurality of projecting features of nanoscale extent or separation,
but the molding surface can also be a smooth planar surface, as for
planarization. The improved method can be practiced without
mechanical presses and without sealing the region between the mold
and the substrate.
Inventors: |
Chou, Stephen Y.;
(Princeton, NJ) ; Zhang, Wei; (Plainsboro,
NJ) |
Correspondence
Address: |
GLEN E. BOOKS, ESQ.
LOWENSTEIN SANDLER PC
65 LIVINGSTON AVENUE
ROSELAND
NJ
07068
US
|
Assignee: |
PRINCETON UNIVERSITY
|
Family ID: |
46299322 |
Appl. No.: |
10/445578 |
Filed: |
May 27, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10445578 |
May 27, 2003 |
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10244276 |
Sep 16, 2002 |
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10244276 |
Sep 16, 2002 |
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10046594 |
Oct 29, 2001 |
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10244276 |
Sep 16, 2002 |
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10140140 |
May 7, 2002 |
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10140140 |
May 7, 2002 |
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09618174 |
Jul 18, 2000 |
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6482742 |
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60382961 |
May 24, 2002 |
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Current U.S.
Class: |
264/402 ;
264/320; 425/174; 425/406 |
Current CPC
Class: |
B29C 43/56 20130101;
B29C 2043/3211 20130101; B29C 59/022 20130101; B29C 43/021
20130101; B29C 2043/025 20130101; B29C 43/36 20130101; G03F 9/7053
20130101; B29C 33/62 20130101; B29C 2043/568 20130101; B29C 59/026
20130101; B29C 2059/023 20130101; B29C 43/003 20130101; B29C 43/52
20130101; G03F 7/0002 20130101; B82Y 10/00 20130101; B82Y 40/00
20130101 |
Class at
Publication: |
264/402 ;
264/320; 425/174; 425/406 |
International
Class: |
B29C 043/02 |
Claims
What is claimed:
1. A method for processing a moldable surface comprising the steps
of: providing a substrate having the moldable surface; providing a
mold having a molding surface; pressing the molding surface and the
moldable surface together by electric or magnetic field-induced
pressure to imprint the molding surface onto the moldable surface;
and withdrawing the mold from the moldable surface.
2. The method of claim 1 wherein the moldable surface comprises one
or more moldable layers disposed on the substrate.
3. The method of claim 2 wherein the imprinting produces reduced
thickness regions in the moldable layer and further comprising the
steps of: removing the material of the moldable layer from the
reduced thickness regions to selectively expose regions of the
substrate; and further processing the substrate selectively in the
exposed regions.
4. The method of claim 3 wherein the further processing comprises
doping the substrate with impurities, removing material from the
substrate, or adding material on the substrate.
5. The method of claim 1 further comprising the step of hardening
the moldable surface after pressing.
6. The method of claim 1 wherein the substrate or the mold or both
are sufficiently flexible to conform together under the
pressure.
7. The method of claim 2 where the thickness of the moldable layer
is in the range 0.1 nm to 200 .mu.m.
8. Apparatus for imprinting a moldable surface on a substrate
comprising: a mold having a molding surface; a substrate having a
moldable surface positioned adjacent the molding surface of the
mold; a first chargeable or conductive layer disposed distal to the
moldable surface/molding surface interface on the mold side of the
interface; a second chargeable or conductive layer disposed distal
to the moldable surface/molding surface interface on the moldable
surface side of the interface; and means for forming an electrical
field between the first and second layers to press the molding
surface and the moldable surface together.
9. The apparatus of claim 8 wherein at least one of the first and
second layers is conductive and the means for forming an electrical
field comprises a voltage source.
10. The apparatus of claim 9 wherein the first and second layers
comprise conductive material.
11. The apparatus of claim 9 wherein the voltage source comprises a
DC voltage source.
12. The apparatus of claim 9 wherein the voltage source comprises
an AC voltage source.
13. The apparatus of claim 9 wherein the voltage source comprises a
pulsed voltage source.
14. The apparatus of claim 9 wherein the voltage source can provide
a combination of DC, AC and pulsed voltage.
15. The apparatus of claim 9 wherein the mold includes a conductive
layer.
16. The apparatus of claim 10 wherein the voltage source is
connected between the layers of conductive material.
17. The apparatus of claim 9 wherein the mold and the substrate are
disposed between at least two external electrodes and the means for
forming an electrical field comprises a voltage source to apply a
voltage between the external electrodes.
18. The apparatus of claim 17 wherein the voltage source is an AC
or pulsed voltage source.
19. Apparatus for imprinting a moldable surface on a substrate
comprising: a mold having a molding surface; a substrate having a
moldable surface positioned adjacent the molding surface; a
magnetic layer disposed distal to the moldable surface/molding
surface interface; and a magnetic field generator to generate a
magnetic field interacting with the first magnetic layer to press
the molding surface and the moldable surface together.
20. The apparatus of claim 19 wherein the magnetic layer comprises
a conductive coil or spiral.
21. The apparatus of claim 19 wherein the magnetic field generator
comprises a conductive coil or spiral.
22. The apparatus of claim 19 wherein the magnetic layer comprises
a layer of magnetized material.
23. The apparatus of claim 19 wherein the magnetic layer comprises
a layer of magnetizable material.
24. The method of claim 1 further comprising the step of applying
imprint pressure mechanically or as direct fluid pressure.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 60/382,961 filed by Stephen Chou and Wei
Zhang on May 24, 2002 and entitled "Field-Induced Pressure Imprint
Lithography".
[0002] This application is a continuation-in-part of U.S. patent
application Ser. No. 10/244,276 filed by Stephen Chou on Sep. 16,
2002 and entitled "Lithographic Method For Molding Pattern With
Nanoscale Features" which, in turn, is a continuation of U.S.
application Ser. No. 10/046,594 filed by Stephen Chou on Oct. 29,
2001, which claims priority to U.S. patent application Ser. No.
09/107,006 filed by Stephen Chou on Jun. 30, 1998 (now U.S. Pat.
No. 6,309,580 issued Oct. 30, 2001) and which, in turn, claims
priority to U.S. application Ser. No. 08/558,809 filed by Stephen
Chou on Nov. 15, 1995 (now U.S. Pat. No. 5,772,905 issued Jun. 30,
1998). All of the foregoing Related Applications are incorporated
herein by reference.
[0003] This case is also a continuation-in-part of U.S. patent
application Ser. No. 10/140,140 filed by Stephen Chou on May 7,
2002 and entitled "Fluid Pressure Imprint Lithography" which is a
divisional of U.S. patent application Ser. No. 09/618,174 filed by
Stephen Chou on Jul. 18, 2000 and entitled "Fluid Pressure Imprint
Lithography" (now U.S. Pat. No. 6,482,742).
FIELD OF THE INVENTION
[0004] This invention relates to imprint lithography and, in
particular, to imprint lithography wherein electrical or magnetic
fields are used to imprint a molding surface onto a moldable
surface. The process is particularly useful to provide nanoimprint
lithography of enhanced resolution and uniformity over an increased
area.
BACKGROUND OF THE INVENTION
[0005] Photolithography is a key process in the fabrication of
semiconductor integrated circuits and many optical, magnetic and
micromechanical devices. Lithography creates a pattern on a thin
film carried on a substrate so that, in subsequent process steps,
the pattern can be replicated in the substrate or in another
material which is added onto the substrate. Conventional
lithography typically involves applying a thin film of resist to a
substrate, exposing the resist to a desired pattern of radiation,
and developing the exposed film to produce a physical pattern. In
this approach, resolution is limited by the wavelength of the
radiation, and the equipment becomes increasingly expensive as the
feature size becomes smaller.
[0006] Imprint lithography, based on a fundamentally different
principle, offers high resolution, high throughput, low cost and
the potential of large area coverage. In imprint lithography, a
mold with microscale or nanoscale features is pressed into a thin
film, deforming the shape of the film according to the features of
the mold and forming a relief pattern in the film. After the mold
is removed, the thin film can be processed to remove the reduced
thickness portions. This removal exposes the underlying substrate
for further processing. Details of imprint lithography are
described in applicant's U.S. Pat. No. 5,772,905 issued Jun. 30,
1998 and entitled "Nanoimprint Lithography". The '905 patent is
incorporated herein by reference.
[0007] The usual method of pressing the mold into the thin film
involves positioning the mold and the substrate on respective rigid
plates of a high precision mechanical press. With such apparatus,
the process can generate sub-25 nm features with a high degree of
uniformity over areas on the order of 12 in.sup.2. Larger areas of
uniformity would be highly advantageous to increase throughput and
for many applications such as displays.
[0008] The use of a high precision mechanical press to press a mold
into a thin film presents tolerance problems in replicating small
patterns over large areas. Presses move on guide shafts through
apertures, and the spacings between the shafts and their respective
apertures can be large compared to the features to be replicated.
Such spacings permit undesirable relative translational and
rotational shifts between the substrate and the mold. Moreover,
despite the most careful construction, the molds and the substrates
used in lithography are not perfectly planar. When these molds and
substrates are disposed on the rigid plates of a press, the
deviations from planarity over large areas can result in variations
in the molding pressure and depth of imprint. Accordingly, it is
desirable to provide a method of imprint lithography which avoids
the limitations of mechanical presses.
[0009] An alternative method of pressing the mold into the thin
film is the technique of fluid pressure imprint lithography
described in applicant's U.S. Pat. No. 6,482,742 issued Nov. 19,
2002 and entitled "Fluid Pressure Imprint Lithography". In this
method the molding surface is disposed adjacent the film, the
molding surface/film interface is sealed and pressurized fluid is
used to force the molding surface into the film. Since the pressure
is isostatic, translational and rotational shifts are minimal, and
smaller features can be imprinted with high uniformity over larger
areas than can be imprinted using mechanical presses.
[0010] Fluid pressure imprinting has dramatically improved
nanoimprint lithography. A further improvement for commercial
manufacture would be a method which could provide comparable
results without the necessity of sealing the molding surface/film
interface.
SUMMARY OF THE INVENTION
[0011] An improved method of imprint lithography involves using
field-induced pressure from electric or magnetic fields to press a
mold into a substrate having a moldable surface. In essence, the
method comprises the steps of providing a substrate having a
moldable surface, providing a mold having a molding surface and
pressing the molding surface and the moldable surface together by
electric or magnetic fields to imprint the molding surface onto the
moldable surface. The molding surface advantageously comprises a
plurality of projecting features of nanoscale extent or separation,
but the molding surface can also be a smooth planar surface, as for
planarization. The improved method can be practiced without
mechanical presses and without sealing the region between the mold
and the substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The advantages, nature and various additional features of
the invention will appear more fully upon consideration of the
illustrative embodiments now to be described in detail in
connection with the accompanying drawings. In the drawings:
[0013] FIG. 1 is a schematic flow diagram of the steps in an
improved method of imprint lithography;
[0014] FIG. 2 illustrates apparatus for practicing the method of
FIG. 1 using an electrical field;
[0015] FIGS. 3A, 3B and 3C show various substrate constructions for
facilitating electrical contact with a substrate conductive
layer;
[0016] FIG. 4 shows an alternative apparatus for practicing the
method of FIG. 1 without direct electrical contact;
[0017] FIG. 5 illustrates apparatus for practicing the method of
FIG. 1 using a magnetic field;
[0018] FIGS. 6A and 6B show exemplary multilayer mold constructions
useful for the apparatus of FIGS. 2, 4 and 5; and
[0019] FIG. 7 schematically illustrates how the method of FIG. 1 is
compatible with a variety of other processing steps.
[0020] It is to be understood that these drawing are for purposes
of illustrating the concepts of the invention and are not to
scale.
DETAILED DESCRIPTION
[0021] Referring to the drawings, FIG. 1 is a schematic flow
diagram of an improved process for imprint lithography using
field-induced pressure. An initial step shown in Block A, is to
provide a mold having a molding surface such as plurality of
protruding features and a substrate having a surface of moldable
material such as one or more moldable thin films. Protruding
features are preferably micrometer scale features and, more
advantageously, nanoscale features. The method is highly
advantageously where the mold surface has at least two spaced apart
protruding features. A moldable material is one which retains or
can be hardened to retain the imprint of the protruding features
from the mold surface.
[0022] The next step, shown in Block B, is to place the mold
adjacent the moldable surface. If the moldable surface is a thin
film that already includes a previously formed pattern, then the
pattern of the mold should be carefully aligned with the previous
pattern. This can be done by alignment techniques well known in the
art.
[0023] The third step (Block C) is to press the mold onto the
moldable surface by field-induced pressure. One method for doing
this is to dispose the assembly between conductive layers and apply
an electrical field between the layers. Another approach is to
dispose the assembly between layers of magnetic material and to
apply a magnetic field that will force the layers together. The
advantage of field-induced pressure is that the resulting force
uniformly pushes the mold onto the moldable surface. Shear or
rotational components are de minimus. Moreover since the mold
and/or substrate are flexible rather than rigid, conformation
between the mold and the moldable surface is achieved regardless of
unavoidable deviations from planarity. The result is an enhanced
level of molding resolution, alignment and uniformity over an
increased area of the film.
[0024] The next step shown in Block D, is to harden the moldable
surface, if necessary, so that it retains the imprint of the mold
and then to remove the mold. The process for hardening depends on
the material of the moldable surface. Some materials will maintain
the imprint with no hardening. Thermoplastic materials can be
hardened by preliminarily heating them prior to molding and
permitting them to cool after imprint. PMMA, for example, can be
suitably softened by heating to 120.degree. C. prior to molding and
hardened by cooling after imprint. Heat curable materials can be
hardened by applying heat during imprint. A heater and/or the use
of a heated pressurized fluid can thus effectuate such softening or
hardening. Radiation curable materials can be hardened by the
application of UV radiation during imprint. Silicon can be softened
by UV laser radiation to accept imprinting and hardened by cooling
to ambient temperature.
[0025] The fifth step shown in Block E is optional in some
applications. It is to remove contaminants (if any) and excess
material from the recesses of the molded surface. The molded
surface will typically have raised features and recesses. In many
lithographic operations it is desirable to eliminate the material
from the recesses so that the underlying substrate is exposed for
further processing. This can be conveniently accomplished using
reactive ion etching.
[0026] In some applications, the imprinted structure itself is a
part of a device to be built. In other applications the resulting
structure is a resist-covered semiconductor substrate with a
pattern of recesses extending toward the substrate. Such a
structure can be further processed in a variety of ways well-known
in the art. For example, the molded film can be used as a mask for
the removal of surface layers in exposed regions of the substrate,
for doping exposed regions of the substrate or for growing or
depositing materials on the exposed regions.
[0027] FIG. 2 schematically illustrates a first exemplary apparatus
9 for practicing the method of FIG. 1. The apparatus 9 comprises an
assembly of a mold 10 having a molding surface 12 and a substrate
20 having a moldable surface 22. The mold and substrate are
disposed with the molding surface 12 adjacent the moldable surface
22. The mold 10 comprises a body having a molding surface 12.
Surface 12 can include a plurality of protruding features 13 having
a desired shape for imprinting onto the moldable surface 22. The
molding surface 12 can be patterned into protruding features 13 of
nanoscale dimensions by known techniques such as electron beam
lithography. The projecting extent of the protruding features 13 is
typically in the range 0.1 nm to 200 .mu.m. Typical separations
between protruding features are 200 nanometers or less.
Advantageously the mold 10 is a multilayer structure comprising a
layer of conductive or chargeable material that is distal to the
interface between the molding surface and the moldable surface. The
term layer as used herein is intended broadly to cover a supported
layer, a plate or a composite layer.
[0028] The substrate 20 is typically a solid substrate and the
moldable surface 22 is typically a thin film of polymer, monomer,
olgimer or combination thereof that is pliable or can be made
pliable to pressure and can retain a pressure-imprinted deformation
or pattern. It can be a thermoplastic polymer, such as
polycarbonate or polymethyl methacrylate (PMMA), which softens in
response to heat. Alternately it can be a monomer liquid, such as a
curable silicone, which hardens with curing. Yet further in the
alternative, it can be solid silicon which can be liquefied by a UV
laser pulse. Polymer thin films are typically applied to the
substrate by spraying or spinning. Advantageously the film does not
adhere to the mold surface. If necessary, the mold surface can be
coated with a release agent to prevent such adherence.
Advantageously the substrate is a multilayer structure comprising a
layer or plate 23 of conductive or chargeable material that is
distal to the molding surface/moldable surface interface.
[0029] The pressure between the mold and the substrate can be
generated by electrical or magnetic forces between the mold and the
substrate. For a pressure generated by an electrical force, an
attractive electrical field can be established between the mold and
the substrate. Alternatively a repulsive field can be used to drive
the mold and the substrate together. For a pressure generated by a
magnetic force, an attractive magnetic force between the mold and
the substrate can provide attractive pressure or repulsive external
magnetic forces can drive the mold and the substrate together.
[0030] In use, a field forces the molding surface onto the moldable
surface. In the embodiment of FIG. 2 where the field is an electric
field, this imprinting can be effected by connecting layers 14 and
23 to opposite polarity terminals of a voltage source 30. The
voltage from source 30 can be AC, DC, pulsed, or a combination of
such voltages.
[0031] Electrical connection with layers 14 and 23 can be
facilitated by choosing substrate 20 to be conductive and mold 10
to be conductive. Alternatively, conductive through holes (not
shown) through substrate 20 to layer 23 and through mold 10 to
layer 14 can provide connection. FIGS. 3A, 3B and 3C show substrate
constructions that facilitate electrical connection with substrate
conductive layer 23. In FIG. 3A, electrical contact can be made
from the bottom of substrate 20 through conductive vias 30. In FIG.
3B electrical contact can be made from the bottom or from the
lateral edges by coating or plating a peripheral layer 31 of
conductive material around a portion of the lateral periphery of
the substrate 20. A similar peripheral conductive layer 32 is shown
in FIG. 3C except that layer 32 does not extend to the bottom of
the substrate. Yet further in the alternative, an electric field
for imprinting the substrate can be created between appropriately
dissimilar materials by the use of light, heat or RF radiation.
[0032] In some applications it may be advantageous to make the mold
10 or the substrate 20 (including the conductive layers) of
materials at least partially transparent to radiation which can be
used to soften or cure the moldable surface.
[0033] In other applications it may be desired to omit one of the
conductive layers 14, 23 and to use an attractive or repulsive
field between an external electrode and the remaining layer to
force the molding surface and the moldable surface together.
[0034] FIG. 4 shows an alternative apparatus for using an
electrical field to press the molding surface into the moldable
surface. The apparatus of FIG. 4 is similar to that of FIG. 2
except that rather than directly connecting the layers 14 and 23 to
a voltage source, the mold 10/substrate 20 assembly is disposed
between electrodes 40 and 41 that are connected to an AC voltage
source 42. The frequency of the AC source can be tuned to generate
a desired induced voltage between layers 14 and 23.
[0035] FIG. 5 illustrates alternative apparatus for practicing the
method of FIG. 1. The FIG. 5 apparatus is similar to the apparatus
of FIG. 2 except that instead of conductive layers, magnetic layers
14A, 23A are disposed distal to the mold/substrate interface and a
magnetic field is used to imprint the mold surface into the
moldable surface. The magnetic layers can be magnetizable material,
permanent magnets or electromagnets. For example, layers 14A, 23A
can comprise helically or spirally wound coils. Current from
current sources 50A, 50B applied to coils can produce an attractive
magnetic field to press the molding surface onto the moldable
surface. Connections between the current sources and their
respective coils can be facilitated by conduction through
conductive vias (not shown) in the substrate and the mold. In a
modified form, layers 14A and 23A can be magnetic materials that
attract one another, and the current sources can be omitted. In
another variation, the mold can comprise an electromagnet and the
substrate can comprise a layer of magnetizable or permanent
magnetic material or vice versa. In essence, what is needed is a
magnetic layer and a magnetic field generator interacting with the
magnetic layer to press the molding surface and the moldable
surface together.
[0036] FIGS. 6A and 6B show different multilayer mold constructions
useful in the embodiments of FIGS. 2-5. In FIG. 6A, the conductive
or magnetic layer 14 is disposed immediately distal to the
interface between the molding surface 12 and the moldable surface
(not shown). In FIG. 6B, the conductive or magnetic layer 14 is
still distal to the interface on the mold side, but there is an
intervening layer 60.
[0037] It is further contemplated that field-induced imprinting can
be used in conjunction with other methods of providing imprint
pressure such as direct fluid pressure or mechanical pressure in
all possible permutations in applying these forces, including
applying them simultaneously, sequentially, or selectively.
[0038] FIG. 7 schematically illustrates additional steps compatible
with the process described herein. Precision mechanical pressing or
pressurized fluid pressing can be of supplemental use, particularly
after the molding surface is engaged with the moldable layer.
Radiation, such as infrared or ultraviolet, can be used for
heating, softening, or curing the moldable surface material. The
layers 14, 23 can be conductive or magnetic, and the pressing
fields can be DC, AC, or combinations thereof.
[0039] It is to be understood that the above described embodiments
are illustrative of only a few of the many embodiments which can
represent applications of the invention. Numerous and varied other
arrangements can be made by those skilled in the art without
departing from the spirit and scope of the invention.
* * * * *