U.S. patent application number 16/137717 was filed with the patent office on 2019-09-26 for system and methods of mold/substrate separation for imprint lithography.
This patent application is currently assigned to Nanonex Corporation. The applicant listed for this patent is Nanonex Corporation. Invention is credited to Stephen Y. CHOU, Lin HU, Hua TAN.
Application Number | 20190294040 16/137717 |
Document ID | / |
Family ID | 51538550 |
Filed Date | 2019-09-26 |
View All Diagrams
United States Patent
Application |
20190294040 |
Kind Code |
A1 |
TAN; Hua ; et al. |
September 26, 2019 |
SYSTEM AND METHODS OF MOLD/SUBSTRATE SEPARATION FOR IMPRINT
LITHOGRAPHY
Abstract
A nanoimprint system and methods for separating imprinted
substrates with nano-scale patterns from mold for manufacturing.
Generally, the system includes means to create, monitor, and
control relative movement between the mold and substrate for
separation. It is capable of controlling where and when the
separation happens and finishes. The relative movement may be
generated by motion stages, springs, stage driven flexures,
inflatable O-rings, gas flow, and other mechanical means. It may be
monitored by separation force, overhead camera, and
vacuum/pressures in different area of the system. The relative
movement may be any combination of stages movements and movement
sequences. The separation speed, direction, and force can be well
controlled in the system to achieve fast and reliable separation
between mold and substrate, and at the same time maintain the
pattern shape and details on the consolidated imprint resist.
Inventors: |
TAN; Hua; (Princeton
Junction, NJ) ; HU; Lin; (Livingston, NJ) ;
CHOU; Stephen Y.; (Princeton, NJ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nanonex Corporation |
Monmouth Junction |
NJ |
US |
|
|
Assignee: |
Nanonex Corporation
Monmouth Junction
NJ
|
Family ID: |
51538550 |
Appl. No.: |
16/137717 |
Filed: |
September 21, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14776607 |
Sep 14, 2015 |
10108086 |
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PCT/US2014/030655 |
Mar 17, 2014 |
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16137717 |
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61799856 |
Mar 15, 2013 |
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61791491 |
Mar 15, 2013 |
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61799681 |
Mar 15, 2013 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B29C 43/58 20130101;
G03F 7/0002 20130101; B29C 59/026 20130101; B29C 43/50 20130101;
B29C 43/56 20130101; B29C 2043/5833 20130101; B82Y 10/00 20130101;
B29C 2043/563 20130101; B29C 59/022 20130101; B29C 2043/5808
20130101; B82Y 40/00 20130101; B29C 2043/5891 20130101 |
International
Class: |
G03F 7/00 20060101
G03F007/00; B82Y 10/00 20060101 B82Y010/00; B29C 43/50 20060101
B29C043/50; B29C 43/56 20060101 B29C043/56; B29C 43/58 20060101
B29C043/58; B29C 59/02 20060101 B29C059/02; B82Y 40/00 20060101
B82Y040/00 |
Claims
1. A method of separating a mold and an imprinted substrate in
imprint lithography comprising the steps of: providing an assembly
of a mold having a molding surface imprinted into a substrate
having a moldable surface at the mold/substrate interface; and
generating a controlled relative movement between the substrate and
mold.
2. The method of claim 1 wherein the relative movement is generated
by multi axis motion stages having at least one of a Z, a pitch,
and a roll basic motions.
3. The method of claim 2 wherein the motion to generate relative
movement can be a single motion throughout the separation process,
or it can be a combination of different motions at different phase
of the separation, where the speed and acceleration of motions in
any time can be controlled to assist the separation.
4. The method of claim 3 wherein the single motion can be a one
axis movement, or a two axis movement at the same time, or a three
axis movement at the same time, where the three moving axis is a Z,
a pitch and a roll.
5. The method of claim 1 wherein the speed of relative motion can
be set to zero at certain period of the separation process to
assist separation.
6. The method of claim 1 wherein the relative movement is generated
by springs, cylinders, inflatable O-rings, or mechanical means
which can generate motion.
7. The method of claim 1 wherein the relative movement is generated
by fluid flow, the fluid pressure, flow rate and flow direction
being controllable to assist the separation and a flow direction
being controlled to be vertical to the separation front to assist
the separation.
8. The method of claim 1 wherein the separation speed and direction
are controlled by a monitoring of the separation force.
9. The method of claim 1 wherein the separation completion may be
decided by a factor selected from the group consisting of a sudden
change of separation force, a vacuum reading of substrate and mold
holding chucks, and an image of separation boundary.
10. The method of claim 1 wherein the separation force for
different moldable material is measured, the suitable moldable
materials selected to minimize the separation force during the
separation.
11. A system for separating a mold and an imprinted substrate in
imprint lithography comprising: a mold holding fixture for holding
a mold having a mold surface with nanostructures; a substrate
holding fixture for holding a substrate having a molding surface; a
stage assembly having three axis movement; a contact force sensors
positioned for sensing the separation force between the moldable
surface and the molding surface during separation; an overhead
camera for observation of separation boundary; and at least one
vacuum pump;
12. A system for separating a mold and an imprinted substrate in
imprint lithography comprising: a mold holding fixture for holding
a mold having a mold surface with nanostructures; a substrate
holding fixture for holding a substrate having a molding surface; a
stage assembly having three axis movement; a contact force sensors
positioned for sensing the separation force between the moldable
surface and the molding surface during separation; a chamber
housing defining a chamber having at least a mold held by the mold
holding fixture and the substrate held by the substrate holding
fixture positionable therein, the chamber housing configured
enabling the applying of a pressure inside the chamber that is
higher and/or lower than atmospheric pressure; a pressure regulator
and a manifold each being fluidly coupled to the chamber for
changing the pressure inside the chamber; a gas reservoir of high
pressure, a regulator and piping to allow the high pressure gas; at
least one vacuum pump; an overhead camera for observation of
separation boundary; and means to divide the chamber into two
fluidly separate sub-chambers, each sub-chamber being configured
for a separate controlled sub-chamber environment including a
separate pressure and/or vacuum, a separate gas content, and a
separate gas flow rate into and out thereof.
13. The method of claim 12 wherein both bending of the mold and
peeling substrate away from the mold, or a mixture of them can be
carried out for separation.
14. The method of claim 12 wherein the separation location, speed,
and time can be controlled and monitored.
15. A method of patterning a substrate with microstructure and
nanostructure patterns in roller imprint lithography comprising the
steps of: applying moldable material on the substrate surface;
providing a mold having a molding surface with the patterns; at
least one of the moldable or the molding surfaces is part of a
roller, or at least one backside of the mold and the substrate is
contacting a roller; contacting the moldable surface with the
molding surface and press; and curing the contacted area and
separate;
16. The method of claim 15 wherein the press is provided by fluid
pressure.
17. The method of claim 15 wherein there is at least one chamber is
used for fluid pressure.
18. The method of claim 15 wherein the substrate is driving by
rollers.
19. The method of claim 15 wherein the moldable material is
deposited on the surface of the substrate by material dispensing
head, or by moving the substrate through the liquid material, or by
contacting the substrate with a roller already coated with the
material.
20. The method of claim 15 wherein the surface of the substrate may
be coated with thin layer of material by vapor. The vapor is
generated by heating a chemical.
21. The method of claim 15 wherein the moldable material thickness
on the surface of the substrate may be controlled by a thickness
controller placed close to the substrate and take away extra
material.
22. The method of claim 15 wherein the press pressure can be
controlled by the input pressure in the ACP head, the distance from
the head to the moldable surface, and the base pressure controllers
set up on the roller belt.
23. A system for patterning substrate surfaces with microstructure
and nanostructure patterns in roller imprint lithography
compromising: a mold having a mold surface with the patterns; a
substrate having a molding surface; contact force sensors
positioned for sensing the force at different locations of the
roller system; at least a chamber housing configured enabling the
applying of a pressure inside the chamber that is higher and/or
lower than atmospheric pressure; or a ACP head enabling the
applying of a pressure on the output of the head; a pressure
regulator and a manifold each being fluidly coupled to the chamber
for changing the pressure inside the chamber or coupled to the ACP
head to change the output pressure of the head; a gas reservoir of
high pressure, a regulator and piping to allow the high pressure
gas; at least one vacuum pump; moldable material dispensing head,
or moldable material bath in contact with at least a section of the
substrate, or a roller in contact with the substrate and moldable
material; a vapor treatment chamber to coat vapor of chemicals on a
section of the mold or the substrate; rollers to move at least one
of substrate and mold; and means to control the thickness of the
moldable materials by contacting and taking away extra
materials;
24. The system of claim 23 wherein ACP head consists of a housing
with one end open; a light reflector; lens for focusing and
expanding light; a UV light source, a thermal light source, or an
combination of both; and at least an opening hole for fluid
coupling to the high pressure supply.
25. A method of patterning a roller mold with microstructure and
nanostructure patterns comprising the steps of: having a substrate
with the patterns on the surface; coating roller mold with
surfactant coating; roll the mold on the substrate patterned
surface with a controlled pressure, so the pattern on the substrate
is transferred to the mold surface; removing the surfactant coating
exposed in the air; plating the roller mold with metal; rotating
the roller mold to polish its surface so that the patterns are
exposed in the air and the metal surface is smooth; and removing
the remaining surfactant and patterns transferred initially from
the substrate.
26. The system of claim 25 wherein removing the surfactant coating
can be completed by a special designed cylindrical RIE chamber
where roller is one electrode and chamber is grounded. The RIE
chamber can selectively remove the surfactant on the roller surface
that is not covered by the pattern transferred from the substrate.
The RIE chamber can then etch the patterns into the roller.
27. A method of patterning a roller mold with microstructure and
nanostructure patterns comprising the steps of: coating the roller
surface with photoresist; using projection optics with UV light and
photomask to exposure a line of the resist on the surface of the
roller; rotating the roller to next field and run exposure again;
keeping rotating and exposure each time until all required areas on
the roller surface are exposed; placing roller into a developer to
remove unwanted resists; and etching the pattern into the roller
using a wet etching or a dry etching.
28. A method of patterning a roller mold with microstructure and
nanostructure patterns comprising the steps of: having a substrate
with the molding pattern on the surface; coating a roller surface
with moldable material; and contacting and rotating the roller with
the substrate under a controlled pressure and curing the resists
while rotating.
29. A method of patterning a roller mold with microstructure and
nanostructure patterns comprising the steps of: having a flexible
substrate with the molding pattern on the front surface; coating
the roller surface, the back surface of the substrate, or both with
either glue or a magnetic material; and rotating the roller on the
back surface of the substrate to wrap the substrate around the
roller;
30. A system for patterning substrate surfaces with microstructure
and nanostructure patterns in step and repeat imprint lithography,
compromising: a mold having a molding surface with the patterns; a
substrate having a molding surface not smaller than the patterning
area of the mold; a gantry for holding mold holder; a multi-axis
stages; contact force sensors positioned for sensing the forces
during imprint and separation; a pressure regulator and a manifold
each being fluidly coupled to the system; a gas reservoir of high
pressure, a regulator and piping to allow the high pressure gas; at
least one vacuum pump; a material dispensing system for placing
moldable material on the substrate; a vibration control table; a
robot system with cassettes for automatically loading and unloading
of substrates and molds; a microscopic system for measuring the
spatial relation between the mold and the substrates at multiple
locations; a UV exposure light and reflective optics; a mold holder
which has center opening and can change the mold size in the XY
plane; and means to press one area of the substrate using the mold
at a time, then separate and continue with other areas.
31. The system of claim 30 wherein dispensing system further
includes a gantry, a resist dropping head, resist observation
microscopes, a camera, a light source, a resist cleaning station, a
resist reservoir, driving electronics and software, a multiple axis
stages to control vertical dropping gap and resist droplet spacing
on substrate.
32. The system of claim 30 wherein the moldable material may be
placed on the substrate as droplets uniformly, or according to the
pattern density on the mold, or arranged in a way so the adjacent
droplets can merge together to drive out air quickly.
33. The system of claim 30 wherein the mold holder can change the
mold size using piezo drives, or air cylinder with accurate
pressure control.
34. The system of claim 30 wherein the substrate can be a standard
wafer of 4'', 6'', 8'', 12'', or 16'' with material ranging from
Silicon, semiconductor, and other optical material, and the mold
can be a standard quartz plate of 6'' by 6'' by 0.25'' thickness
with a smaller die size in the center, raised as a pedestal with
height 1-50 um.
35. A method of patterning a substrate with microstructure and
nanostructure patterns in step and repeat imprint lithography
comprising the steps of: providing a mold having a molding surface
with the patterns; applying moldable material on an area of the
substrate surface; adjusting the gaps between the mold and the
substrate so the moldable surface and molding surface is in
parallel; approaching the substrate to the mold while aligning them
according to the alignment marks on the mold and the substrate;
contacting the moldable surface with the molding surface; applying
pressure and hold a certain time; curing the contacted area;
separating the moldable surface from molding surface with patterns
left on the moldable surface; and moving to next area and repeating
the pressing again until all areas of the moldable surface is
patterned.
36. The method of claim 35 wherein the mold may have a much thinner
center area.
37. The method of claim 36 wherein a quartz plate may be bonded
with the back surface of the mold to form a mini-chamber inside the
mold.
38. The method of claim 37 wherein the mini-chamber can be used to
apply a fluid pressure on the mold front pattern surface during
imprint.
39. The method of claim 37 wherein the mini-chamber can be used to
apply a fluid pressure on the mold front pattern surface to bend it
and drive the air out before imprint.
40. The method of claim 37 wherein the mini-chamber can be used to
apply a fluid pressure on the mold front pattern surface to bend it
after imprint to separate the surface from the moldable surface on
the substrate.
41. The method of claim 35 wherein the mold may have an inflatable
area on the front surface. The inflatable area may be inflated to
either seal off the moldable surface and molding surface before
imprint, or to separate the mold from substrate after imprint.
42. The method of claim 41 wherein the sealed off area between the
moldable and molding surfaces can be vacuumed to remove the air
between the surfaces.
43. The method of claim 35 wherein a localized pressure can start
from the center of the molding surface and propagate to the edge of
the molding surface to squeeze the air between the moldable surface
and molding surface out.
44. The method of claim 43 wherein the localized pressure can be
generated by sending fluid pressure to the vacuum grooves either on
the mold holder, or on the substrate holder, or both.
45. The method of claim 43 wherein the localized pressure can be
generated by electrical field established between the moldable
surface and molding surface.
46. The method of claim 35 wherein a fast diffusion gas such as
helium may be used to drive out the air.
47. The method of claim 35 wherein holes on the mold, closing to
the patterns edge are made to allow helium, vacuum pumping, or
other gas flowing. The purpose is to help driving out the air
before imprint and separating after imprint.
48. The method of claim 35 wherein the separation completion is
detected by at least one of a sudden change of vacuum reading of
substrate or mold holders, a sudden change of recorded separation
force, and an imaging observation of contacting area disappearing;
or by a combination of these methods.
49. The method of claim 35 wherein the separation may be carried
out by a relative motion between the substrate and the mold wherein
the relative motion is generated by the multi-axis stages, or
bending from localized pressure, or inflatable area on the mold
surface, or local gas flow, or a combination of these methods.
50. The method of claim 35 wherein the separation force, speed and
direction can be controlled using sensors, stages, and cameras,
wherein a minimized separation force profile is used for
separation.
51. The method of claim 35 wherein a low evaporation rate moldable
material is dispensed on the substrate and the low evaporation rate
enables the coating of all the area of the surface with moldable
material at a time before imprint.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Applications Nos. 61/791,491, 61/799,681, and 61/799,856, each of
which were filed on Mar. 15, 2013, the disclosure of which is
incorporated herein by reference.
FIELD
[0002] The present disclosure relates to system and methods for
roller imprint lithography. It is particularly useful for fast mass
production of substrates with replication of patterns from a mold
having microscale or nanoscale features by imprint lithography,
including roller imprint lithography.
BACKGROUND
[0003] The statements in this section merely provide background
information related to the present disclosure and may not
constitute prior art.
[0004] Nanoimprint lithography, also often called imprint
lithography, is capable of replicating patterns on a pre-made mold
as small as several nanometers. The pre-made mold has extruded
areas and recessed areas on its replication surface, which
constitute patterns of various shapes and sizes. The mold was
typically made by a patterning step using electron beam lithography
(EBL) or mixing of EBL and optical lithography, and, a follow-up
etching step using reactive ion etching (RIE) to create the
patterns. Nanoimprint lithography starts from applying a volume of
polymer onto a substrate by either spinning or dispensing. The
polymer is either flowable in ambient temperature, or, from rigid
to deformable or flowable by thermally heating. Then, the pre-made
mold is positioned to contact with the substrate. After that, the
mold is pressed against the substrate. If the polymer is in liquid
in ambient temperature, pressing the mold against the substrate
will force the surface extrusion areas on the mold replication
surface to go into the layer of the polymer. If the polymer is
rigid in ambient temperature, a thermally heating step is conducted
prior to the contact, after the contact but before the pressing, or
during the pressing to make the polymer deformable or flowable.
Thus, pressing the mold against the mold is able to force the
surface extrusion areas on the mold replication surface to go into
the layer of the polymer. When the extruded areas completely go
into the layer of the polymer, the polymer is transited from
deformable or flowable into rigid by UV radiation, thermally
heating or thermally cooling depending on types of the polymer. At
last, the mold is released from the substrate while the layer of
the polymer attaches to the substrate. To prevent the polymer from
sticking to the mold, a very thin release coating may be deposited
on the replication surface of the mold. Typical release coating
included surface release surfactant and per-fluoro polymer
deposited by CVD. After the substrate is separated from the mold,
the extrusion areas on the mold surface are corresponding to the
recessed areas in the polymer layer. Therefore, a reverse-tone
replication of the patterns on the mold is formed onto the polymer
film on the substrate. The polymer may be a thermo-plastic polymer
or curable polymer. A thermo-plastic polymer transits from rigid to
deformable or flowable when being heated above its glass transition
temperature, and, vice versus when is cooled below its glass
transition temperature. A curable polymer is deformable or flowable
originally, and transit to rigid when being heating to curing
temperature for thermo-set type or being cured under UV exposure
for UV-curable type. When alignment is needed, the mold is aligned
with the substrate through a set of matching align markers prior to
the contact. Previously, electron beam lithography is very slow to
write nanoscale patterns. It is unlikely to use it for mass
production of nanoscale devices. Nanoimprint lithography is able to
replicate whole area of patterned surface of the pre-made mold onto
the substrate by one cycle of the process. It can dramatically
increase the efficiency of patterning nanoscale features. Because
the mold is repeatedly used for many cycles of imprinting, the high
cost of using electron beam lithography to make the mold is
averaged into these many imprints. Nanoimprint lithography delivers
a practical method to produce nanoscale devices at low cost.
[0005] Since its invention in 1995 by Stephen Y. Chou (referring to
U.S. Pat. No. 5,772,905), nanoimprint lithography has successfully
demonstrated its capability of replicating a feature as small as 5
nm. Meanwhile, many research works were carried out on developing
resists for imprinting, mold making techniques, mold release
coating for clean separation, and apparatus to do imprinting. In
overall, nanoimprint lithography has evolved into being a widely
used technology for research laboratories, but not reached a stage
ready to meet much higher requirements of industrial use. One of
the improvements needed for industrial use is an effective method
to separate imprinted substrate from mold with high throughput and
no damage to the patterns.
[0006] Fast nanoimprint apparatus with capability to separate mold
and substrate automatically is highly demanded by semiconductor,
magnetic media, and other industries to use this technology to
manufacture micro-scale and nano-scale device products. Previously
a fast nanoimprint apparatus was used to deform the mold to
separate it from the substrate after imprint. (U.S. patent
application Ser. No. 13/011,844) The setup was placed in a chamber
where a deformable mold is fixed firmly around its full periphery.
In the patent, the mold has to be deformable, which limits the
thickness and material of the mold to be used. The loading and
unloading of the mold is difficult giving the fact that the
periphery of the mold are fixed firmly. In addition, the separation
motion of the substrate is in the Z direction only. There is
nothing to monitor the separation process, which could be important
in a manufacturing environment.
[0007] Nanoimprint lithography, also often called imprint
lithography, is capable of replicating patterns on a pre-made mold
as small as several nanometers. The pre-made mold has extruded
areas and recessed areas on its replication surface, which
constitute patterns of various shapes and sizes. The mold was
typically made by a patterning step using electron beam lithography
(EBL) or mixing of EBL and optical lithography, and, a follow-up
etching step using reactive ion etching (RIE) to create the
patterns. Nanoimprint lithography starts from applying a volume of
polymer onto a substrate by either spinning or dispensing. The
polymer is either flowable in ambient temperature, or, from rigid
to deformable or flowable by the tally heating. Then, the pre-made
mold is positioned to contact with the substrate. After that, the
mold is pressed against the substrate. If the polymer is in liquid
in ambient temperature, pressing the mold against the substrate
will force the surface extrusion areas on the mold replication
surface to go into the layer of the polymer. If the polymer is
rigid in ambient temperature, a thermally heating step is conducted
prior to the contact, after the contact but before the pressing, or
during the pressing to make the polymer deformable or flowable.
Thus, pressing the mold against the mold is able to force the
surface extrusion areas on the mold replication surface to go into
the layer of the polymer. When the extruded areas completely go
into the layer of the polymer, the polymer is transited from
deformable or flowable into rigid by UV radiation, thermally
heating or thermally cooling depending on types of the polymer. At
last, the mold is released from the substrate while the layer of
the polymer attaches to the substrate. To prevent the polymer from
sticking to the mold, a very thin release coating may be deposited
on the replication surface of the mold. Typical release coating
included surface release surfactant and per-fluoro polymer
deposited by CVD. After the substrate is separated from the mold,
the extrusion areas on the mold surface are corresponding to the
recessed areas in the polymer layer. Therefore, a reverse-tone
replication of the patterns on the mold is formed onto the polymer
film on the substrate. The polymer may be a thermo-plastic polymer
or curable polymer. A thermo-plastic polymer transits from rigid to
deformable or flowable when being heated above its glass transition
temperature, and, vice versus when is cooled below its glass
transition temperature. A curable polymer is deformable or flowable
originally, and transit to rigid when being heating to curing
temperature for thermo-set type or being cured under UV exposure
for UV-curable type. When alignment is needed, the mold is aligned
with the substrate through a set of matching align markers prior to
the contact. Previously, electron beam lithography is very slow to
write nanoscale patterns. It is unlikely to use it for mass
production of nanoscale devices. Nanoimprint lithography is able to
replicate whole area of patterned surface of the pre-made mold onto
the substrate by one cycle of the process. It can dramatically
increase the efficiency of patterning nanoscale features. Because
the mold is repeatedly used for many cycles of imprinting, the high
cost of using electron beam lithography to make the mold is
averaged into these many imprints. Nanoimprint lithography delivers
a practical method to produce nanoscale devices at low cost.
[0008] Since its invention in 1995 by Stephen Y. Chou (referring to
U.S. Pat. No. 5,772,905), nanoimprint lithography has successfully
demonstrated its capability of replicating a feature as small as 5
nm. Meanwhile, many research works were carried out on developing
resists for imprinting, mold making techniques, mold release
coating for clean separation, and apparatus to do imprinting. In
overall, nanoimprint lithography has evolved into being a widely
used technology for research laboratories, but not reached a stage
ready to meet much higher requirements of industrial use. One of
the improvements needed by industrial use is imprint system and
method with high throughput and overlay accuracy.
[0009] Fast nanoimprint apparatus is highly demanded by
semiconductor, magnetic media, and optics industries to use this
technology to manufacture nano-scale device products. However,
traditional nanoimprint lithography is still improving the
throughput, and certain application requires very large (a few
meters) substrate, which is difficult for traditional nanoimprint
lithography to provide.
[0010] Roller Imprint Lithography, offering a much simpler
nanoimprint lithography machine design, much higher throughput, and
lower cost, is a very attractive alternative to traditional
nanoimprint. Since its invention in 1998 (Referring to "Roller
Nanoimprint Lithography" paper on J. Vac. Sci. Technol. B 16(6)),
various research efforts have been dedicated to the roller
nanoimprint. To fully utilize the potential of the roller
nanoimprint, some of the key areas still need further improvement.
These include: a) to make an ultra-high quality and uniform
imprint; b) have ways to place on a roller with microscale or
nanoscale patterns which can then continuously imprint the
substrate.
[0011] Optical lithography techniques are currently used to make
most microelectronic devices. However, it is believed that these
methods are reaching their limits in resolution. Sub-micron scale
lithography has been a critical process in the microelectronics
industry. The use of sub-micron scale lithography allows
manufacturers to meet the increased demand for smaller and more
densely packed electronic circuits on chips. It is expected that
the microelectronics industry will pursue structures that are as
small as or smaller than about 50 nm. Further, there are emerging
applications of nanometer scale lithography in the areas of
opto-electronics and magnetic storage. For example, photonic
crystals and high-density patterned magnetic memory of the order of
terabytes per square inch may require sub-100 nm scale
lithography.
[0012] For making sub-50 nm structures, optical lithography
techniques may require the use of very short wavelengths of light
(e.g., about 13.2 nm). At these short wavelengths, many common
materials are not optically transparent and therefore imaging
systems typically have to be constructed using complicated
reflective optics. Furthermore, obtaining a light source that has
sufficient output intensity at these wavelengths is difficult. Such
systems lead to extremely complicated equipment and processes that
may be prohibitively expensive. It is also believed that
high-resolution e-beam lithography techniques, though very precise,
are too slow for high-volume commercial applications.
[0013] Nanoimprint lithography, also often called imprint
lithography, is capable of replicating patterns on a pre-made mold
as small as several nanometers. The pre-made mold has extruded
areas and recessed areas on its replication surface, which
constitute patterns of various shapes and sizes. The mold was
typically made by a patterning step using electron beam lithography
(EBL) or mixing of EBL and optical lithography, and, a follow-up
etching step using reactive ion etching (RIE) to create the
patterns. Nanoimprint lithography starts from applying a volume of
polymer onto a substrate by either spinning or dispensing. The
polymer is either flowable in ambient temperature, or, from rigid
to deformable or flowable by thermally heating. Then, the pre-made
mold is positioned to contact with the substrate. After that, the
mold is pressed against the substrate. If the polymer is in liquid
in ambient temperature, pressing the mold against the substrate
will force the surface extrusion areas on the mold replication
surface to go into the layer of the polymer. If the polymer is
rigid in ambient temperature, a thermally heating step is conducted
prior to the contact, after the contact but before the pressing, or
during the pressing to make the polymer deformable or flowable.
Thus, pressing the mold against the mold is able to force the
surface extrusion areas on the mold replication surface to go into
the layer of the polymer. When the extruded areas completely go
into the layer of the polymer, the polymer is transited from
deformable or flowable into rigid by UV radiation, thermally
heating or thermally cooling depending on types of the polymer. At
last, the mold is released from the substrate while the layer of
the polymer attaches to the substrate. To prevent the polymer from
sticking to the mold, a very thin release coating may be deposited
on the replication surface of the mold. Typical release coating
included surface release surfactant and per-fluoro polymer
deposited by CVD. After the substrate is separated from the mold,
the extrusion areas on the mold surface are corresponding to the
recessed areas in the polymer layer. Therefore, a reverse-tone
replication of the patterns on the mold is formed onto the polymer
film on the substrate. The polymer may be a thermo-plastic polymer
or curable polymer. A thermo-plastic polymer transits from rigid to
deformable or flowable when being heated above its glass transition
temperature, and, vice versus when is cooled below its glass
transition temperature. A curable polymer is deformable or flowable
originally, and transit to rigid when being heating to curing
temperature for thermo-set type or being cured under UV exposure
for UV-curable type. When alignment is needed, the mold is aligned
with the substrate through a set of matching align markers prior to
the contact. Previously, electron beam lithography is very slow to
write nanoscale patterns. It is unlikely to use it for mass
production of nanoscale devices. Nanoimprint lithography is able to
replicate whole area of patterned surface of the pre-made mold onto
the substrate by one cycle of the process. It can dramatically
increase the efficiency of patterning nanoscale features. Because
the mold is repeatedly used for many cycles of imprinting, the high
cost of using electron beam lithography to make the mold is
averaged into these many imprints. Nanoimprint lithography delivers
a practical method to produce nanoscale devices at low cost.
[0014] Since its invention in 1995 by Stephen Y. Chou (referring to
U.S. Pat. No. 5,772,905), nanoimprint lithography has successfully
demonstrated its capability of replicating a feature as small as 5
nm. Meanwhile, many research works were carried out on developing
resists for imprinting, mold making techniques, mold release
coating for clean separation, and apparatus to do imprinting.
Overall nanoimprint lithography has evolved into being a widely
used technology for research laboratories, but not reached a stage
ready to meet much higher requirements of industrial use. One of
the needed improvements however as identified by the present
inventors is for industrial use is step and repeat imprint system
and method with good imprint uniformity, high throughput and
overlay accuracy.
SUMMARY
[0015] The embodiments of this disclosure include systems and
methods to separate substrates from mold after imprint resist
solidification. Generally, the system has an apparatus to hold mold
and an apparatus to hold substrate. A hollow mold holder is fixed
to the top inner surface of the chamber and positioned underneath
the transparent top section. By changing the type of mold holders
used in the system, molds of different materials or different sizes
and thicknesses may be fixed to the mold holder and carry out
imprint. More specifically, transparent, semi-transparent or opaque
molds (all referring to visible wavelength) may be used in the
system for nanoimprint. An enclosed volume referring to mold
mini-chamber is formed between the mold/holder and top wall of the
chamber. Inside chamber, a stage assembly, leveling apparatus, and
force sensing apparatus are installed. A chuck to vacuum hold a
substrate is mounted on top of the stage assembly. At beginning of
the imprinting, the substrate with a layer of resist is positioned
underneath the mold at a predetermined gap between them. Then, the
substrate is moved up to contact with the mold either under vacuum,
under atmosphere or under pressure from a mixture of different
gases. The substrate and mold may be pressed further by introducing
higher pressure inside the chamber. After consolidating the resist,
the substrate is separated from the mold by motions enabled by
stage movements, or by deforming the mold enabled by differential
pressure between the mold mini-chamber and the bulk volume of the
chamber, or a mixing of both.
[0016] The disclosed systems, apparatuses and methods relate to
high throughput and high speed continuous producing of micro-scale
and nano-scale patterns using roller nanoimprint lithography
(RNIL). Generally, the roller system is modular: it has a section
for resist coating and a section for nanoimprint. Unwinding roller
and rewinding roller are located on the two ends of the system.
[0017] The key component of the system is a special designed Air
Cushion Press (ACP) head with LTV/Thermal heating source. It is
capable of applying fluid pressure at the same time curing the
resists. At the nanoimprint section, the mold will contact with the
substrate with an adjustable base pressure. The ACP head will apply
a uniform pressure where the resist is cured.
[0018] This disclosure demonstrated ways to apply air cushion press
to six forms of roller molds and substrates, which includes rigid
flat mold, roller mold, flexible mold, rigid substrate, and
flexible substrate.
[0019] This disclosure also demonstrated ways to apply resist
coating on the substrate surface. A resist coating wheel may be
used to contact the resist first, and then rotate to contact
substrate, bring the resist to the surface of substrate. A resist
thickness controller will be able to control the resist coated. A
different coating method uses dispensing head to place low
viscosity (0.1-200 cP) resist droplets on the surface of substrate.
Vapor treatment may be used to help the adhesion.
[0020] This disclosure further demonstrated five different ways to
pattern roller molds with micro-scale and nano-scale features.
[0021] This disclosed system and methods include forming a layer on
a region of a substrate. It includes, inter alia, positioning a
liquid on a substrate and contacting the liquid with the mold to
carry out imprint. Upon separation, the process will continue until
all regions of the substrate are patterned by the mold. Substrates
with micro-scale and nano-scale patterns can be mass produced using
the system and methods.
[0022] A multi-axis robot is used to transfer the imprint molds and
substrates to the chamber. Multiple and different end effectors may
be mounted on the same robot to handle molds and substrates of
different foam factors. Positions and orientations of molds and
substrates may be adjusted at different stations in the system.
Before imprint, the molds are adjusted with the patterned side
facing down, while the substrates are adjusted with the patterned
side facing up. After all the imprints are finished, the molds may
be adjusted with the patterned side facing up before placing back
into the mold cassette.
[0023] Further aspects of the present disclosure will be in part
apparent and in part pointed out below. It should be understood
that various aspects of the disclosure may be implemented
individually or in combination with one another. It should also be
understood that the detailed description and drawings, while
indicating certain exemplary embodiments, are intended for purposes
of illustration only and should not be construed as limiting the
scope of the disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The features, nature and advantages of this disclosure will
be more clearly understood by consideration of the illustrative
embodiments now to be described in detail in connection with the
accompanying drawing. In the drawing:
[0025] FIG. 1 is schematic drawing of the system illustrating one
exemplary embodiment.
[0026] FIG. 2 is a schematic drawing illustrating the process
chamber.
[0027] FIG. 3 is a top view schematic drawing of the imprinted area
illustrating the separation process.
[0028] FIG. 4A-4D illustrates operation process of the apparatus
illustrating one exemplary embodiment;
[0029] FIG. 5 is a flow chart to show steps of separation
process.
[0030] FIG. 6 is a schematic drawing illustrating the substrate
surface during separation process.
[0031] FIG. 7 is a schematic drawing illustrating the process
chamber with ultrafine multi-axis stages.
[0032] FIG. 8 is schematic drawing showing a typically roller
imprint system.
[0033] FIG. 9 is a schematic drawing illustrating the air cushion
press head integrated with the UV/Thermal heating source.
[0034] FIG. 10 illustrates a roller system using air cushion press
for imprint rigid mold on flexible substrate;
[0035] FIG. 11 illustrates a roller system using air cushion press
for imprint flexible mold on flexible substrate.
[0036] FIG. 12 illustrates a roller system using air cushion press
for imprint roller mold on rigid substrate.
[0037] FIG. 13 illustrates a roller system using air cushion press
for imprint rigid mold on rigid substrate.
[0038] FIG. 14 illustrates a roller system using air cushion press
for imprint flexible mold on rigid substrate;
[0039] FIG. 15 illustrates a roller system using air cushion press
for imprint roller mold on flexible substrate;
[0040] FIG. 16 illustrates the process of using plating to make a
roller mold with microscale and nanoscale patterns.
[0041] FIG. 17 illustrates the process of using a special RIE to
make a roller mold with microscale and nanoscale patterns.
[0042] FIG. 18 illustrates the process of using projection optics
exposure to make a roller mold with microscale and nanoscale
patterns.
[0043] FIG. 19 illustrates the process of using cured resists to
make a roller mold with microscale and nanoscale patterns.
[0044] FIG. 20 illustrates the process of using thin flexible Ni to
make a roller mold with microscale and nanoscale patterns.
[0045] FIG. 21 illustrates a roller system using chamber for fluid
pressure press.
[0046] FIG. 22 illustrates chamber design in a roller system using
fluid pressure press.
[0047] FIG. 23 illustrates chamber design in a roller system using
fluid pressure press.
[0048] FIG. 24 illustrates chamber design in a roller system using
fluid pressure press.
[0049] FIG. 25 is a schematic drawing of the system illustrating
one exemplary embodiment.
[0050] FIG. 26 is a schematic drawing illustrating the side view of
the dispenser system.
[0051] FIG. 27 illustrates the apparatus for observation resist
dispensing.
[0052] FIG. 28 illustrates the front view of the resist dispenser
system.
[0053] FIG. 29 illustrates a mold and substrate holder structure
with a special designed mold.
[0054] FIG. 30 illustrates a special designed mold structure.
[0055] FIG. 31 illustrates a design and process for electrical
field assisted dropping resist merging.
[0056] FIG. 32 illustrates the magnification control apparatus of
the system.
[0057] FIG. 33 illustrates the contact between magnification
control and the side of the mold.
[0058] FIG. 34 is a schematic drawing of the alignment apparatus of
the system.
[0059] FIG. 35 illustrates a special designed mold structure using
O-ring and gas gap sensor.
[0060] FIG. 36 illustrates an imprint mold design with gas gap
sensor integrated.
[0061] FIG. 37 illustrates a dispenser system for placing moldable
material on substrates.
[0062] It is to be understood that these drawings are for purposes
of illustrating the concept of the invention and are not to
scale.
[0063] It should be understood that throughout the drawings,
corresponding reference numerals indicate like or corresponding
parts and features.
DETAILED DESCRIPTION
[0064] The following description is merely exemplary in nature and
is not intended to limit the present disclosure or the disclosure's
applications or uses.
[0065] The descriptions assume that UV curable imprint is conducted
if it is not clearly identified and UV curable imprint is used as
example. However, the invention does not limit for UV curable
imprint and also apply for thermo-plastic imprint. An ordinary
skilled in the art that is familiar with nanoimprint technology can
easily revise the embodiment described in the invention to
implement the concept of the invention for all type of
imprinting.
[0066] The overall separation process of the system is illustrated
in FIG. 1. The invention described method of separate mold and
substrate after imprint by generating a controlled relative
movement between them. The relative movement may be the peeling:
either peeling substrate from mold, or peeling mold from substrate,
while controlling the peeling direction and peeling speed. Even
thick mold/substrate with hard materials can be separated after
imprint under the process.
[0067] In accordance with the concept of the invention, referring
to FIG. 2, the relative movement may be generated by motion stages.
An imprint system compatible with the peeling process using motion
stages includes a minimum of two axis stage (Z-Pitch or Z-Roll),
preferable three axis (Z-Pitch-Roll). The complete system is
controlled by control system and PCs. A mold 300 for imprinting is
held against a mold holder 200 by using vacuum or other mechanical
clamp means. The mold holder is hollow to permit a central
patterned region 310 of mold 300 to be freely accessible from
underneath side, top side or both sides. The surfaces in contact
with the mold on the mold holder 200 are designed and specially
polished, which can hold the mold with a minimum deformation. A
stage assembly 210 is mounted onto the bottom. The stage assembly
210 contains X-Y-Z-Yaw (.theta.)-Pitch-Roll six degree motion
controls for many purposes: first, the multi-axis motion of 210 may
provide adjustment to make the surface of substrate 320 parallel to
the patterned surface of the mold 300. Second, the multi-axis
motion of 210 may be used to move the substrate 320 to align with
the mold 300. Third, the multi-axis stage may be used to bring the
substrate 320 to contact with the mold 300 before imprint. Last,
the multi-axis stage 210 may be used to separate the substrate 320
from mold 300 after imprint. An optional overhead camera 1110 is
used to observe the separation boundary between the separated and
un-separated area between the mold and substrate.
[0068] A chuck 230 with vacuum grooves on its top surface is
mounted on a force sensing apparatus 220 which in turn is mounted
on the stage assembly 210. A substrate 300 for imprinting is held
on chuck 230 by vacuum pumping through the vacuum grooves.
Additionally, apparatus 225 is used to clamp the substrate long the
plane X-Y by mechanical means. Surface of chuck 230 are designed
and specially polished in order to hold the substrates with minimum
deformation. The stage assembly is either mechanically installed or
capable of moving the substrate within its X-Y travel ranges to
superimpose the center of the substrate with the center of
patterned region 310 in X-Y plane. The substrate may have a
moldable material 340 applied on its side surface facing the mold
before imprint begins. The moldable material could be a continuous
film layer of imprinting resist spun on or a plurality of droplets
of imprinting resist dispensed on. When the moldable material is in
form of a plurality of droplets before imprinting, the distribution
of the droplets could be a uniform matrix of equal spacing among
adjacent droplets along one direction or multi directions, or an
arbitrary matrix optimized for merging each to achieve desired
imprinted patterns. In additional to these general demands for
imprinting, the special distribution of droplets is preferred to
deliver a uniform and continuous contacting interface between the
mold and the substrate during the imprint process of the
apparatus.
[0069] Referring to FIG. 4A, mold holder 200 with mold 300
installed is loaded into chamber 100 and firmly attached to top
plate of the chamber wall by mechanical apparatus 201. Substrate
320 with moldable material 340 on its top surface is held against
chuck 230 by pumping through the vacuum grooves and positioned
beneath the opening of mold holder 200. At beginning of the imprint
process of the apparatus, substrate 320 is positioned to a starting
position which normally has a 1-2 millimeter gap between the
substrate and the mold. Gap measuring sensors are used to detect
mold and substrate gaps at 3 different locations. Then the
substrate is adjusted by moving Pitch-Roll-Z stages of 210 until
all the gaps are the same. This means the substrate surface is in
parallel with the mold surface. Alternatively, the gap may be
measured using microscopes and alignment marks on the mold and
substrate. In addition, by observing the interference pattern
between the mold and the substrate, the substrate surface may also
be adjusted to be in parallel with the mold surface.
[0070] Next step of the imprint process is to pump chamber volume
150 and mold mini-chamber 160 to remove air. This pumping step
facilitates to reduce trapped air defects of imprinted patterns.
Alternatively, an extra pneumatic line is equipped with the machine
which allows special gas with fast diffusion such as Helium to be
used to facilitate the removal of air in the chamber.
[0071] Aligning the substrate with the mold can be finished before
the pumping or in the pumping. Normally, aligning the substrate and
the mold is accomplished by positioning an align marker on the
substrate overlapping with a matching align marker on the mold
under microscopes. To prevent possible shift of the substrate on
chuck 230 during the pumping, both the substrate and mold are
mechanically clamped in positions. By using the vertical microscope
and alignment marks on the substrate and mold, the substrate is
first moved to coarsely align with the mold. This will remove the
small error generated during loading and machine assembling, and
make sure the fine alignment marks on the mold and substrate are
located in the same field of view, therefore no further searching
of alignment marks necessary, significantly improving the alignment
speed and reliability, which are required for manufacturing.
Microscopes will then read mis-alignments at different locations by
using the fine alignment marks. The finer X, Y, and rotation error
can be corrected by substrate stages 210 and further by substrate
stages 229.
[0072] Referring to FIG. 4B, the substrate may be moved up to
contact with the mold under a controlled push by the stage
assembly. The substrate 320 surface to be patterned is adjusted in
parallel with mold pattern surface by the leveling mechanism in the
system before the final contact. Optical sensors (not shown) and
force sensors 220 can be used to locate the exact contacting point
and contact force. To accomplish the contact step, substrate 320 is
moved up slowly until there is a slight controllable contact force
between the mold and substrate reached. Final contact can be
achieved either by continuing moving stages 210 or by releasing the
mold from the mold holder. Fluid pressure imprint (ACP) and UV
curing were then carried out.
[0073] FIG. 4C illustrates the separation process where substrate
is peeled off from the mold. FIG. 1 further illustrates this
process in four detailed steps, while FIG. 3 illustrates top view
of imprinted area for each step of the separation shown in FIG. 1.
The methods of separation share a common concept that use either
vacuum or other mechanic means to hold the mold and the substrate,
and create a relative movement between mold and substrate for
separation. Pull the mold/substrate in certain way using the stage
assembly to create relative motion between the mold and substrate
is one way to separate. The mold may or may not need to be
intentionally deformed for the separation. Referring to step 501 of
FIG. 5, first, pressures at both chamber and mini-chamber will be
well controlled. In one example, this pressure is set to be the
same atmosphere pressure. In one more example, the mini-chamber
will have a slightly higher pressure than the chamber so the mold
is bending towards the substrate. In yet another example, the
mini-chamber will have a slightly lower pressure than the chamber
so the mold is bending upwards away from the substrate. The
separation then starts from vacuum holding back side of substrate
320 against top surface of chuck 230 by pumping through the vacuum
grooves on the chuck, and at the same time holding mold 300 against
surface of mold holder 200 by pumping through the vacuum grooves on
the mold holder, as shown in step 502 of FIG. 5. If chuck 230 is
away from the substrate, the chuck is positioned to contact back
side of the substrate by the stage assembly prior to the vacuum
holding.
[0074] Referring to step 503 of FIG. 5, to separate, Z-Pitch-Roll
stages will pull substrate 320 away from the mold staring from one
corner: this can be accomplished by moving Z down while moving the
Pitch and Roll stages accordingly as shown in FIG. 6A. The purpose
of this action is to control the behavior of separation to start
from one corner of the imprinted area. Because both the substrate
and mold are held against the vacuum grooves on the mold holder and
chuck, at beginning of the pull, one corner of the imprinted area
is separated first. Referring to FIG. 3, where the shaded area
shows the resist 350 is still in contact with mold and substrate,
and empty area shows the mold is already separated from the
substrate. The boundary between them is called the separation front
line. As the downward pulling is progressing, the separated region
of the substrate propagates from the firstly separated corner inner
ward the center. At end of the downward pulling, the substrate is
completely separated from the mold as shown in D of FIG. 3. The
speeds, acceleration, deceleration of the Z-Pitch-Roll stages can
be independently fine adjusted to control how fast and the
direction the separation propagates. Thus, the reliability of
separation is significantly improved with the critical dimension of
fine nano-scale patterns in the imprint process maintained. As
force sensors are directly mounted between the stage 210 and the
chuck 230, separation force can be monitored and controlled. The
other advantage of current system is it allows user to measure the
separation force of different resists therefore fine turning their
process parameters for manufacturing. Alternatively, the separation
motion of the substrate can be much more complex than a simple
downward diagonal pulling motion to best separate the substrate
from the mold, reducing the possible damage to nano-scale patterns
and improving separation speed. The stage holding the substrate in
the system is capable of multi-axis motion movements, therefore the
substrate can move with its motion and speed accurately controlled.
The separation may include movements of multiple steps with the
speed and direction of each movement be controlled. In one more
example, the substrate moves down in Z while going through Roll
motion, as shown in FIG. 6B. In another example, the substrate
moves down in Z while going through Pitch motion, as shown in FIG.
6C. The motion shown may also be combined to create more
sophisticated motion profile. In yet another example, the
separation includes 2 step movements: first the substrate moves
down in Z while going through Roll motion, and then it moves down
in Z going through Pitch motion. In fact, any combination of the
stages movements and movement sequence, which helps the separation
front line to propagate, may help the separation and end up
separating mold/substrate. A simple preferable way of separation is
by moving stages Z-Pitch-Roll to have a diagonal separation front
movement. But using Z-Pitch or Z-Roll to generate a separation
front along the substrate direction (X or Y) may also be
acceptable. A combination using Z-Pitch first then Z-Roll, or vice
versa, may also work. During separation, the speed of the relative
movement between mold and substrate can be set to 0, meaning both
mold and substrate can stop at a certain position. This happens
when during separation, we hold and wait for the separation front
line to propagate.
[0075] Another advantage of proposed method is the mold used for
the apparatus may or may not need to be deformable under a
reasonable differential pressure between its two sides. The mold
could be made of quartz, glass, polymer, semiconductor, metal or a
mixture of some of the above materials regardless of the thickness.
One example of the molds uses 150 mm by 150 mm quartz substrate
with a thickness of 6.35 mm; One example of the molds uses 200 mm
diameter Silicon substrate with a thickness of 0.1-2 mm; yet one
more example of the molds uses 8'' diameter quartz or glass wafer
with a substrate thickness of 0.2-1 mm; another example of the mold
uses 12'' diameter quartz or glass wafer with a substrate thickness
of 0.2-2 mm; one more example of the mold uses 8'' diameter Ni
substrate with a thickness of 0.1-1 mm.
[0076] Yet another advantage of the method is there is no
requirement on the relative sizes and thickness of the mold and
substrate. The mold can be bigger, smaller, or the same size as the
substrate. There is no requirement on their respective thickness as
well.
[0077] One more advantage of the method is it does not require the
pressure difference for separation. Therefore it is not necessary
to have a chamber. The chamber in the invention is only used for
imprint purpose.
[0078] The relative movement for separation may also be generated
by springs, stage driven flexures, inflatable O-rings and other
mechanical means. The relative movement may also be generated by
gas flow. When one corner of the mold/substrate is started to
separate, gas flow can be introduced in between mold/substrate,
preferably vertical to the direction of separation front. The flow
rate and gas pressure can be controlled for best result. A mixture
of above methods will work. For example, an inflatable O-ring (in
the mold holder, mold, or substrate holder) may push locally the
corner of the imprinted die to create an initial separation. Then
an air flow, preferably vertical to the separation front line, can
be used to assist the propagation of the separation.
[0079] The current method is also capable of telling when the
separation is finished. The separation completion may be detected
by vacuum of system and mold/substrate holders: for example, when
vacuum levels of mold/substrate holders suddenly get better, it
typically means a separation. The separation may also be detected
by the recorded force during separation. It may also be detected by
processing the camera images from top view of the die area and
locating the separation front line. A combination of these methods
will give reliable indication of the separation.
[0080] Referring to FIG. 7, to further improve the performance of
the separation, higher resolution (nano-scale accuracy) multi-axis
stages 229 may be installed in the system, between substrate chuck
230 and force sensing apparatus 220. Stages 229 serves two
purposes: first, they can move the substrate to achieve ultrafine
alignment to the mold, which are required for manufacturing by many
applications; second, they provide extra fine movement for the
separation process. Different type of stages may be used, including
piezo stages, linear stages, etc. Chamber 100 is not needed for
this purpose.
[0081] The system described here also has an additional function:
it is capable of separating the mold from substrate by deforming
the mold, as described in U.S. patent application Ser. No.
13/011,844. This separation method may be combined with the stage
peeling method to further facilitate the separation process. With a
chamber existing, current system structure also allows for the
automatic robotic arms to load the mold into the chamber, and
unload the mold from the chamber, something difficult in previous
patent application. Therefore we are proposing an imprint system
capable of bending mold for separation, peel substrate for
separation, and a mixture of both. The chamber, the mini-chamber
and the substrate chuck are all fluid connected to separated gas
lines, so their pressure and vacuum, and gas flow may be well
individually controlled. There is a high pressure gas reservoir,
regulators, vacuum pump source, manifold as well used in the
system.
[0082] The improvements possessed by the invention are emphasized
again herein. The apparatus embodiments described in the invention
accomplish a full cycle of imprinting inside the chamber through a
process essentially involving separating the substrate from mold
after imprint by the stage assembly. The speed to finish separation
process is primarily decided by stage response. Using state-of-art
stage technology, stage response can be very fast and capable of
responding to requests in milliseconds. Furthermore, the method is
compatible with the advantageous Air Cushion Press (ACP), which
provides very uniform imprinting force crucial to achieve the
pattern fidelity required by manufacturing.
[0083] It is to be understood that the above described embodiments
are illustrative of only a few of the many embodiments that 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.
[0084] In accordance with the concept of the invention, referring
to FIG. 8, the roller imprint system has at least two modular
sections: one for resist application, including 800, 801, 802 and
rollers for directing directions, one for imprint, including 803,
805, 806, and 807. Alternatively, the substrate may directly pass
through the material path where the material is deposited on its
surface. Extra section may be added between 800 and 804 to allow
the substrate to pass through, where a chemical vapor is deposited
on the surface of the substrate. This may be accomplished by a
small chamber where the chemical is heated. Unwinding roller 804
and rewinding roller 811 are located on the two ends of the system.
Base pressure adjuster 808 and 810 are located at different
sections of the system to control the base contract pressure.
Optionally additional process sections may be inserted after
imprint section: for example, a metal coating section 809 may be
inserted. Alternatively the coating may also be carried out using
vapor treatment. In addition, contact force sensors are installed
in the system close to the roller belt to sense the base pressure
of the press.
[0085] In the resist deposition section, different ways can be used
to coat the substrate. The first method is to use a roller 800 to
pick up resists from a reservoir. By rotating and contacting the
roller with the substrate 820, resists can be transferred to the
substrate. To further control the thickness and uniformity of the
resist, a resist thickness controller 802 maybe used before
imprint. Resist may also be dispensed on the substrate using a
dispenser head 801. Typically a low viscosity resist (0.1-200 cP)
may be used. The nozzle can be moved to have a gap of 0.1 mm-25 mm
to the substrate for dispensing. Typical resist droplets have a
volume of 1-100 pL. By using a dispensing head with multiple
nozzles (16-256), and firing of droplets at >10 KHz, the
droplets can be coated on the substrate on the fly, satisfying the
high speed of roller imprint. As the width of the dispenser head is
from 1''-4'', substrate with width wider than 4'' would need
multiple heads. The firing frequency f (Hz) of the dispenser head
and the moving speed v (m/s) of the roller substrate will determine
the gap between droplets along substrate moving direction to be:
v/f*1e6 (.mu.m). To further assist the resist stickiness with the
substrate, surface surfactant may be applied to the substrate
before the coating. This can be easily done by a vapor treatment of
the substrate. A heated surfactant reservoir is typically placed
underneath the moving substrate for coating. The same vapor
treatment method can also be used to coat the mold.
[0086] In the imprint section, substrate will be in contact with
the mold 803. The base contact may be adjusted by a sensor and
tightening adjustor 808. The fluid pressure can be applied by an
Air Cushion Press (ACP) head 807. The ACP head can be placed very
close to the imprinting roller where a very thin line of resists
will be further imprinted by fluid pressure and then cured.
[0087] Various flexible materials may be used as the substrate or
mold, organic materials including PET, ETFE, PVC, by way of
example, may be used. Low tensile strength and high elongation are
the general properties to look for while searching for new
materials.
[0088] Referring to FIG. 9, which shows a detailed schematic of the
special designed integrated ACP head and light source. The head has
an outside wall 910, gas inlet 950 at the wider end, and an opening
output end where the head is getting much narrower. This works as
an air knife to generate a much higher pressure at the output end.
Inside the head, a UV light source 902 may be placed to generate UV
light for exposure. The source is placed on the focus point of a
reflective mirror at the back of the head. The light will reflect
and then be bent at the lens 960 with its beam direction at the
output end adjusted. By changing the optics inside, the distance
from output beam focus points 901 to the head output plane 970 may
be adjusted. Due to the nature of gas pressure, the head is capable
of uniformly imprint a rectangular area which may have the same
width as the substrate, and a length range of 0.05-1 mm. A thermal
heat source may also be placed inside to replace the UV light. It
is also possible to place both thermal and UV sources inside. In
the imprint process, they can run simultaneously or one after
another.
[0089] The wavelength of UV is typically between 180-410 nm. Narrow
band filters may be used in the light path to limit the wavelength.
.about.365 nm light may be used for exposure. In addition, UV LED
light source may also be used. It typically has a central
wavelength of 365 nm or 400 nm. It has a long lifetime, constant
power density, and can instantly be turned on and off.
[0090] If thermal heating source is to be used, the ACP head may
need to be cooled, preferably by cooling water around the outside
surface 910 of the head.
[0091] During imprint, the ACP head will be placed in close
proximity to the substrate to be imprinted, at a preferred distance
ranging from 0.001-5 mm. The pressure applied depends on the
distance, and the input pressure. The system use high pressure
reservoir, regulators, gas lines and vacuum to control the
pressure. There will be a PC to drive all the control electronics
to move the rollers at controlled speed, and control each section
of the system to finish the imprint work and unwinding/winding.
Sensors are mounted at different locations of the system to tell
the pressures, the gap between parts etc. The rollers have a
typical size of .about.1 inch diameter, although some individual
rollers (including roller to mount mold or substrate) may have
quite different sizes.
[0092] FIG. 10-15 shows ACP roller system designs for six types of
roller imprint systems (include rigid mold, flexible mold, roller
mold on either rigid substrate or flexible substrate) by using
above ACP head or a chamber. They all have similar PC control,
electronics driving, roller unwinding/winding, sensors, pressure
reservoir, pressure control, gap control, with similar roller
sizes. Some of the system can have roller/substrate moving
continuously, while others may go through a move, then imprint
cycle.
[0093] FIG. 10 shows roller ACP setup for imprinting a rigid mold
and flexible substrate. The substrate is first passing a material
flattening roller set 1002. The resist will be dispensed on the
surface of flexible substrate 1001. The flexible substrate is then
moved into a chamber 1005 where vacuum and pressure can be applied.
The rigid mold 1006 is pressed against the flexible substrate
inside chamber 1005 by air pressure and then curing. By peeling the
mold from the substrate after imprint, the separation can be
completed. This method may also be used to fabricate flexible
mold.
[0094] FIG. 11 shows roller ACP setup for imprinting flexible mold
on flexible substrates. The flexible mold 1116 and two rollers may
be arranged vertically. ACP head 1119 is placed on a place where
the mold is in contact with the substrate 1112. Alternatively, the
two rollers may also be arranged horizontally with them at the same
height. Again, the system has moldable material dispensing head
1111 and the moldable material thickness control 1113.
[0095] FIG. 12 shows roller ACP setup for imprinting roller mold on
rigid substrates. Again, the ACP head 1205 is placed on a place
where the roller mold 1204 is in contact with the substrate 1203.
Push roller set 1206 and 1207 will drive the substrate with given
speed.
[0096] FIG. 13 shows roller ACP setup for imprinting rigid mold on
rigid substrates. The roller 1305 and ACP head 1308 are aligned
first, and then move in the same direction with their movement
synced to give a uniform imprint. Two rollers 1307 were used as
substrate 1303 support while the mold 1306 is spring loaded for
easy separation. The setup will be able to imprint a die section
with the same size as the mold, and then move substrate to the next
section for next die. Therefore the roller system movement is no
longer continuous; instead, it will go through a move, stop
(imprint) cycle.
[0097] FIG. 14 shows roller ACP setup for imprinting flexible mold
on rigid substrates. Two rollers 1452 will rotate to move the
flexible mold 1453 while the ACP head 1456 is placed in the middle
for further imprinting as the substrate is moving.
[0098] FIG. 15 shows roller ACP setup for imprinting roller mold on
flexible substrates 1547. Again, the ACP head 1548 is placed in
center where the roller mold 1543 is in contact with the
substrate.
[0099] Fabricating roller mold is as important as roller imprint
system. Without the roller mold, advantage of roller imprint will
be greatly limited. FIG. 9-13 demonstrated five different methods
of patterning a roller mold with microscale and nanoscale
features.
[0100] FIG. 16 shows the first proposed approach for making
patterns on a metal roller 1600. The process starts with generating
a resist pattern 1602 on a substrate 1601. To help promoting the
pattern transfer, a sticking layer 1603 is first applied to the
metal roller surface either by vapor or by dipping. Then the roller
is rotated on the substrate to transfer the pattern from the
substrate to the roller. The sticking layer is then removed to
exposure the metal surface. After that, plating is carried out
using the metal roller. Roller is then rotated to polish the
surface to be smooth, and the resist remaining 1604 is exposed
outside. Finally the resist and the sticking layer underneath it
are removed leaving metal patterns 1605 on the roller surface.
[0101] FIG. 17 shows the second approach for making patterns on a
metal roller. The process starts with generating a resist pattern
1602 on a substrate 1601. To help promoting the pattern transfer, a
sticking layer 1603 is first applied to the metal roller surface
either by vapor or by dipping. Then the roller is rotated on the
substrate to transfer the pattern from the substrate to the roller.
After that, the roller is placed into a RIE chamber 1701 with metal
roller being one of the electrodes for RF. The other electrode is
chamber, which is grounded. RF power 1703 is applied where
different gases may be introduced into the RIE chamber for dry
etching to remove surfactant first and then etch pattern into the
roller.
[0102] FIG. 18 shows the third approach for making pattern on a
roller. Photoresist 1810 is first coated on the roller 1812. Then
traditional projection optics 1811 with a photo mask 1814 is used
to exposure a section of the photoresist 1813. To get nano-scale
patterns, deep UV wavelength with high NA lens need to be selected.
If the roller diameter is big enough, and exposure section is small
enough, the focus depth of the optics will be larger than that of
the difference of resist to photo mask distance due to the roller
surface curvature. By rotating the roller, all the roller
surrounding area can be UV exposed die by die. After develop, the
pattern will be left on the photoresists. Dry etch (as shown in
FIG. 17) or a wet etch process can follow to etch the pattern into
roller.
[0103] FIG. 19 starts with making a traditional flat mold 1912 with
patterns 1911. A roller 1910 is coated with moldable material 1920.
Then the roller is rotated on the mold for imprint. The resist will
be cured while imprinting. Due to the strong strength and low
surface energy of the resist, it can be directly used as the mold
material for further roller imprint.
[0104] FIG. 20 starts with make a thin and flexible mold with
patterns. It can be a Ni mold (thickness less than 1 mm) or any
other flexible materials including PET, PVC, etc. Then a layer of
magnetic material or sticking material is coated around the roller.
By rotating the roller on the back of the flexible material, the
material will be either attracted or glued and bend around the
roller due to the magnetic force or sticking force. The width of
the flexible mold needs to be smaller than the width of the roller,
while the length of the flexible mold should be slightly smaller
than the circumference of the roller.
[0105] FIG. 21 illustrates an alternative design of the roller
imprint system where fluid pressure press may be carried out inside
the chambers 2101 and 2103. Both mold and substrate uses flexible
materials. Here 2102 is the resist dispensing system to place
moldable material on the substrate. Chamber 2101 is used to
duplicate an initial mold into a flexible material 2104. Then the
patterned 2104 will be passed into a second chamber 2103, and
imprint as a mold the pattern to flexible substrate 2105. Both
chambers 2101 and 2103 can be pressured or vacuumed with their
pressures controllable. High pressure reservoir, vacuum supply, and
regulators are used in the system. Either UV light or thermal
heating, or their mixtures can be used in any of the chambers 2101
and 2103.
[0106] FIGS. 22, 23, 24 further illustrates details of three
different designs inside the chamber where the two different
flexible materials, one for mold and one for substrate, imprint
inside the chamber. The directions where the flexible mold and
substrate move inside the chamber are vertical to each other (one
along X, one along Y). FIG. 2205 is the clamp cylinder to control
the belt. 2203 is the top roller to move the mold. 2302 is the
substrate while 2303 is the mold. 2204, 2301 and 2405 are flat
quartz plates. 2201, 2304, 2403 are small fluid chamber where
imprint pressure will be applied. Generally in the designs, the
fluid pressure from chamber provide the pressing.
[0107] The improvements possessed by the invention are emphasized
again herein. The apparatus embodiments described in the invention
accomplish roller imprinting using gas pressure. The special design
Air Cushion Press (ACP) of the process is carried out for roller
nanoimprint. The ACP not only provides very uniform imprinting
force to achieve high pattern transfer fidelity, but also reduces
possible damage to the imprint molds and substrates, both are
crucial for manufacturing. The invention also provides ways to
fabricate the roller mold, which is crucial for the full potential
of the roller imprint technology.
[0108] It is to be understood that the above described embodiments
are illustrative of only a few of the many embodiments that 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.
[0109] The descriptions assume that UV curable imprint is conducted
if it is not clearly identified and UV curable imprint is used as
example. However, the invention does not limit for UV curable
imprint and also apply for thermo-plastic imprint. An ordinary
person skilled in the art who is familiar with nanoimprint
technology can easily revise the embodiment described in this
disclosure to implement the concept of this disclosure for all type
of imprinting.
[0110] This disclosure includes a system which can carry out high
throughput step-&-repeat imprint: system includes, among other
things, loader, dispenser system (with replaceable cartridge,
resist reservoir and pump), imprint system, magnification control,
gas/vacuum control, motion stages.
[0111] In accordance with the concept of this disclosure, referring
to FIG. 25, the step and repeat system has a gantry 2507 that holds
the mold holder 2516. The gantry is mounted on a vibration
controlled table 2501. A multi-axis robot 2503 with multiple end
effectors 2502 is used to pick up molds and substrates from
cassettes 2504. The cassettes are seated on front loaders 2505. The
complete system is controlled by control system 2520 and PCs. A
separate gantry is used to hold the dispensing system 2560. Top
gantry may have an opening which allows alignment microscopes 2519
and 2515, CCD 2514, and laser gap sensors 2511 to see through. UV
exposure light can also go through. The wavelength of UV is
typically between 180-410 nm. Narrow band filters may be used to
limit the wavelength. .about.365 nm light may be used for exposure.
In addition, UV LED light source may also be used. It typically has
a central wavelength of 365 nm or 400 nm. It has a long lifetime,
constant power density, and can instantly be turned on and off.
[0112] Both substrate 2550 and mold 2500 are held uniformly on
their separate holders with minimum deformation. The substrate may
be a standard 4'', 6'', 8'', 12'' or even 16'' silicon wafer, while
the mold may be a 6''.times.6''.times.0.25'' thick quartz plate.
The substrate may also be a semiconductor wafer or optical material
such as sapphire. The center of the mold has a raised pedestal on
the order of 1-50 um in height. Patterns are etched on top of the
pedestal on the mold surface. The imprint die size, which is also
the size of the raised pedestal, may be rectangular with a size of
.about.1''.times.1'' or .about.1''.times.1.5''. The mold used for
the apparatus may or may not need to be deformable under a
reasonable differential pressure between its two sides. The mold
could be made of quartz, glass, polymer, semiconductor, metal, or a
mixture of some of the above materials. One example of the mold
uses 8'' diameter quartz or glass wafer with a substrate thickness
0.2-2 mm; another example of the mold uses 12'' diameter quartz or
glass wafer with a substrate thickness 0.2-2 mm; one more example
of the mold uses 8'' diameter Ni substrate with a thickness of
0.1-2 mm; yet one more example of the mold uses 200 mm diameter Si
substrate with a thickness 0.1-2 mm.
[0113] The substrate is uniformly held on a substrate holder 2520.
The system has a very long travel range stage 2515, together with
stages 2530 of various moving axis. The travel range of X-Y stages
guaranteed all regions of the substrate can be moved underneath the
mold pedestal for imprint. It also allows the substrate to be moved
under the dispenser system for resist application. The stages also
provide the fine movement required for high accuracy alignment.
Piezo, linear motor or air bearing stages may be used in the
system. They can provide an accuracy of <1 nm. The stages also
provide the Pitch-Roll motion, help making the surface of substrate
to be in parallel with that of the mold. The multiple axis movement
of the stage may be used to create the relative movement between
mold and substrate after the imprint for an easy separation.
[0114] The system has a force sensing apparatus 2510. It is capable
of detecting force from 10 grams to 45 kilograms. The sensitivity
is around 0.5 gram. It serves as a mean to detect the mask and
substrate contact points; it also helps to measure the separation
force and control the separation process. A simple way to control
separation may be to set a maximum value of force during the
separation. Whenever the force is getting larger, the stage will
adjust to minimize it.
[0115] Laser sensors and optical microscopes in the system may be
used to accurately measure the gap between mold and substrate at
three or more locations. This helps to level the surface of
substrate to that of the molding surface of mold, and to locate the
accurate contact height of mold and substrate. In addition, special
gas sensors 3521 may also be used to measure the mold and substrate
gap (referring to FIG. 35).
[0116] Referring to FIG. 26, the side view of the dispenser system,
the dispenser head 2601 is mounted on a rotation stage 2602 for
resist droplet spacing adjustment. It also has a Z stage 2604 to
adjust the head vertical position (Z axis) to dispense on the
substrate, contact with the cleaning station 3703, and for camera
observation of the resist droplets. A resist reservoir and pump is
also attached to the head for continuous supply of resists during
manufacturing. The dispenser head has 256 or 512 nozzles with a
natural spacing 128, 256, or 512 um between them. There is also a
long travel stage 2616 on the dispenser gantry 2605 which is
vertical to the long substrate stage. They provided the necessary
movement in X-Y to dispense on substrate.
[0117] Referring to FIG. 27, which is a resist dispensing
observation system. A LED light source 2702 is used as illumination
for the microscope and camera 2701. To avoid exposure of UV
resists, a yellow filter is installed on the light source. The
light source is synced with the frequency where the resist droplets
are fired from the dispenser head, so the droplets can be seen and
captured by the camera. By adjusting the dispensing profile
(include the frequency, driving voltages, voltage profiles), an
optimized and uniform dropping on substrate can be achieved.
[0118] Referring to FIG. 28, which is a front view of the dispenser
system. The substrate 2550 can be brought underneath the head for
dispensing. The gap between head and substrate during dispensing
may be range from 100 um to 25 mm. Each droplet size can range from
1-100 pL. Resist viscosity can range from 1-200 cP. In the center
of the dispensing system is a cleaning pad 2803. It can move in
contact with the bottom of the dispenser head to wipe out the extra
resists to keep it clean. The bottom of the cleaning station 2802
is connected to the exhaust. On the right is the resist observation
station described in detail in FIG. 27.
[0119] There have been a few difficulties of the step-&-repeat
imprint using dispensing resists. First the whole system is in
atmosphere, therefore during imprint, it takes time for the air
between the substrate and mold to go out. Resist droplet merging
may push or dissolve some of the air. However it takes time for the
merging process. Second, a mechanical force is used while the Air
Cushion Press (ACP) has been proved to be the way for uniform
imprint to meet the strict manufacturing requirements of many
applications. FIGS. 29, 30, 31, 35 shows a few approaches to solve
these problems. They may be combined into the current system.
[0120] In our invention, a dropping resist merging and imprint in
air are assisted by localized air pressure (on the back of mold or
substrate). Meanwhile it may also be assisted by localized vacuum
(generated by gas flow) and Helium may also be used.
[0121] Referring to FIG. 29, on both mold holder 2921 and substrate
holder 2925, groups of vacuum/gas grooves are machined. They allow
different area of the mold and substrate to be vacuum and pressured
separately. To remove the air between the mold 2922 and substrate
2924 during imprint, group 1 can be pressured first, then group 2,
3, 4, and 5. This will bend the mold/substrate in the center, then
gradually to the edge. It will squeeze the air out from center to
the edge during resist droplet merging. After resist merging, extra
pressures may be applied to the group of grooves which adds an air
pressure during imprint, improving the imprint uniformity. Usage of
these groups of grooves can also help to bending mold/substrate for
separation after imprint. On the edge of the mold pedestal,
channels 6 are also produced. This serves many functions. First,
when there is a gas flow, it will push the air out, generating a
vacuum in the center die area between the substrate and mold.
Second, Helium gas may be introduced here to help driving air out.
Third, the gas used here may push mold and substrate to bend,
helping separation after imprint.
[0122] Referring to FIG. 30, where a quartz plate 3023 may be
bonded to the back side of a mold 3024. 3023 allows UV light to
pass through to cure the sample. It also allows light to pass
through for alignment. The mold has a very thin thickness in the
center to begin with. After bonding, there is a small mini-chamber
3025 foamed inside the quartz mold. There is no leakage of gas due
to the bonding. As the total thickness of the bonded mold may be
arranged to be the same as 0.25'', the new mold can easily be
loaded/unloaded using existing robot and cassette. The surface of
the new mold may also be patterned with a raised pedestal (not
shown in the figure) with micro or nano scale patterns on top. The
advantage of this arrangement is it allows an air cushion press to
be applied to the thin layer of quartz mold surface, improving the
uniformity; it also allows the center of the mold to bend downwards
contacting the substrate first to squeeze the air out during resist
merging; it further allows the mold surface to be bended, helping
separating mold from the substrate. 3021 can be used for
magnification control of the mold here. 3022 is the mold
holder.
[0123] A dropping resist merging in air may also be assisted by
electrical field. FIG. 31 shows an alternative method to help
dropping resist merge in the air. Different sections of the mold
pedestal area have transparent electrodes that are grouped as 1, 2,
3, 4, and 5. Applying an electrical field between mold and
substrate will generate a force to imprint. By applying e-field in
1 first and then 2, 3, 4, and 5 will imprint center of mold 3107,
then gradually to the edge, which helps to push the air out.
[0124] FIG. 32 shows a magnification control apparatus in the
system. In many applications, change the size of the mold to
correct the dimension variation during various processing steps is
critical. Piezo driven mechanical clamps is used to push the side
surfaces of the mold 300. The force applied by the two piezo
drivers will push the mold against the two mechanical stops on the
other side. By controlling the force applied by the two piezos
3205, the deformation of the mold along X and Y direction can be
controlled. Piezo driving mechanism may also be replaced by any
other fine control movement apparatus. An accuracy air cylinder may
also be used where the force sensor can be integrated on the head
to accurately decide the force applied.
[0125] FIG. 33 further shows detailed structure of the clamp heads
designs. By using compliant flexure structures 3326, 3327, 3324,
and 3325, the head of the clamp is capable of compensating for
minor rotation of mold relative to the push piezos along X, Y and Z
directions, therefore applying a uniform force on the mold. The
distortion of the pattern is minimized.
[0126] FIG. 34 shows the system alignment apparatus. Alignment
apparatus in the system has four microscopes. Three of them are
titled while one of them is vertical. The vertical microscope 3402
has higher NA than the other three titled microscopes, and is used
for coarse alignment of substrates to the mold. The titled
microscopes 3406 will use moire alignment marks on both the mold
and the substrate to read the miss-alignment between them at
different locations. Depending on the type of mold 300 to be used,
the wavelength of illumination lights for the microscopes can be
either in visible (400 nm-800 nm) or IR (800 nm-2000 nm) range. To
prevent illumination lights from exposing the imprint resists, UV
block filters are used in the illumination paths. Alternatively,
two vertical microscopes may also be used for both the coarse and
fine alignment. They will read moire alignment marks from both mask
and substrate.
[0127] FIG. 35 shows an alternative mold structure where seal
O-ring and gas sensor is built into the mold. The special designed
mold with inflatable O-ring 3522 which allows the usage of spin on
resists, and helps dropping resist merging by vacuum out the air
between substrate 3513 and mold 3511. The gas channel 3521 on the
mold can also be used as gas gap sensor. The O-ring also helps with
the separation. The vertical gap sensors 3521 can measure the gap
between the mold and substrate when their gap is less than 250 um.
Multiple sensors at 3 different locations can help substrate
leveling to the mold; it also helps to determine the exact gap
between mold and substrate; in addition, the gas can help pushing
mold and substrate to separate first at a few locations after
imprint. The O-ring in the mold can inflate before the imprint
process, and then groove 6 can help evacuate the air between the
mold and substrate in the center. After that, the O-ring may
graduate retract, with the help of substrate stages to bring
substrate and mold in contact under a local vacuum. Extra advantage
of this design is it will allow the usage of spin on resists. FIG.
36 shows yet another design where the mold 3603 can have through
holes 3602 on it for using as gap sensing and separation.
[0128] In the step and repeat process, a mold for imprinting is
held against a mold holder by using vacuum or mechanical clamp
means. The mold holder is hollow. A central patterned region of
mold to be freely accessible from underneath side, top side or both
sides. The mold holder is securely tightened to the gantry.
Different mold holders may be used to accommodate mold of different
dimensions. The surfaces in contact with the mold on the mold
holder are uniform, which can hold the mold with a minimum
deformation. The mold holder is positioned to have patterned region
exposable through opening section of gantry, and accessible from
underneath.
[0129] A substrate for imprinting is held on chuck by vacuum
pumping through the vacuum grooves. Surface of chuck are designed
and special polished in order to hold the substrates with minimum
deformation. The substrate may have a moldable material applied on
its side surface facing the mold before imprint begins. The
moldable material could be a plurality of droplets of imprinting
resist dispensed on. When the moldable material is in form of a
plurality of droplets before imprinting, the distribution of the
droplets could be a uniform matrix of equal spacing among adjacent
droplets along one direction or multi directions, or an arbitrary
matrix optimized for merging each to achieve desired imprinted
patterns, or optimized to the mold pattern density to get the most
uniform imprint. In additional to these general demands for
imprinting, the special distribution of droplets is preferred to
deliver a uniform and continuous contacting interface between the
mold and the substrate during the imprint process of the
apparatus.
[0130] At each die, at beginning of the imprint process, substrate
is positioned to a starting position which normally has a larger
than 0.5 millimeter gap between the substrate and the mold. Gap
measuring sensors are used to detect mold and substrate gaps at 3
different locations. Then the substrate is adjusted until all the
gaps are the same. This means the substrate surface is in parallel
with the mold surface. Alternatively, the gap may be measured using
microscopes and alignment marks on the mold and substrate. In
addition, by observing the interference pattern between the mold
and the substrate, the substrate surface may also be adjusted to be
in parallel with the mold surface.
[0131] Next the imprint process is to bring mold and substrate
close to carry out alignment. Normally, aligning the substrate and
the mold is accomplished by positioning an align marker on the
substrate overlapping with a matching align marker on the mold
under microscopes.
[0132] By using the vertical microscope and alignment marks on the
substrate and mold, the substrate is first moved to coarsely align
with the mold. This will remove the small error generated during
loading and machine assembling, and make sure the fine alignment
marks on the mold and substrate are located in the same field of
view, therefore no further searching of alignment marks necessary,
significantly improving the alignment speed and reliability, which
are required for manufacturing. If fine alignment (<250 nm) is
required, the 3 titled microscopes will then read mis-alignments at
3 different locations by using the fine alignment marks. The finer
X, Y, and rotation error can be further corrected by substrate
stages.
[0133] The substrate may be moved up to contact with the mold under
a controlled push by the stage assembly while remove the air. The
top moldable surface on substrate is adjusted in parallel with mold
molding surface by the coarse leveling mechanism and optional fine
leveling mechanism stage assembly before the final contact. Laser
sensors and force sensors can be used to locate the exact
contacting point and contact force. To accomplish the contact step,
substrate is moved up slowly until there is a slight controllable
contact force between the mold and substrate reached. then the
substrate is continued moved up by Z while the Pitch and Roll of
the stages are adjusted to keep the contact force low. The initial
contact force prevents relative movement between the mold and the
substrate, therefore maintaining the relative position between
them.
[0134] When the contact step is accomplished, the moldable material
has been pressed lightly and redistributed to fill space between
the mold and the substrate. For case of using very low viscosity
moldable material, the press caused by the contact may be
sufficient to imprint patterns of the mold into the moldable
material. In order to guarantee quality of patterns imprinted, it
may need to apply higher pressure press on the mold and the
substrate than the contact.
[0135] Higher pressure press may be applied on the mold and the
substrate by filling mold mini-chamber with high pressure gas. Air
Cushion Press (ACP) is realized during this step for imprinting.
Details of Air Cushion Press are described by Stephen Y. Chou in
U.S. Pat. No. 6,482,742 under a title of "Fluid Pressure Imprint
Lithography".
[0136] After the moldable material redistributes to completely fill
every space between the mold and the substrate, then, it is
consolidated to solid by a UV exposure. Finally, the high pressure
gas for ACP is vented to atmosphere. So far, pattern formation of
imprinting is completed. The substrate is ready for being released
from the mold.
[0137] One can separate mold and substrate by generating relative
movement between them: this can be accomplished by peeling
substrate from mold; by inflatable O-rings; by gas flow; or by a
combination of these methods. Separation may also be implemented by
bending of mold or substrate, either at an edge, in the center,
either symmetric or non-symmetric.
[0138] The separation can be realized by combining mold deformation
and stage movement. A way to separate the substrate from the mold
starts from positioning chuck underneath substrate at a
predetermined gap. Then, a differential pressure between mold
mini-chamber and air is introduced to deform the mold. As
deformation is enlarged by increasing the differential pressure,
substrate loses contact from the mold starting from die periphery
and expanding toward die center. The differential pressure reaches
a predetermined value so that back side of substrate completely
contacts with chuck. By now, a significant peripheral region of the
substrate is released from the mold and central region of the
substrate is not yet. After that, the substrate is held against
chuck by pumping back side of the substrate through the vacuum
grooves on the chuck surface. Finally, the established differential
pressure is removed to restore the mold backward its original
shape. Because the substrate is vacuum held against the chuck, the
remaining central area of the substrate is separated from the mold.
The substrate stays on chuck after the separation ready for next
die imprint and the mold is returned to its starting status.
[0139] Alternative ways to separate the substrate from the mold are
through the relative movement of mold and substrate. These ways
share a common concept that use both vacuum and mechanic means to
hold the mold and the substrate, and pull the substrate in certain
way using the stage assembly to create the motion to separate. The
mold may be intentionally deformed to further facilitate the
separation. The separation starts from vacuum holding back side of
substrate against top surface of chuck by pumping through the
vacuum groves on the chuck. One way to separate is to pull
substrate downward by moving the stage assembly down. Because the
substrate is held against the vacuum grooves on the chuck and the
mold is deformable, at beginning of the pull, the mold is deformed
so that one corner of the substrate is separated first. As the
downward pulling is progressing, the separated region of the
substrate propagates from the firstly separated periphery inner
ward the center. At end of the downward pulling, the substrate is
completely separated from the mold.
[0140] Alternatively, the separation motion of the substrate can be
much more complex than a simple downward pulling motion to best
separate the substrate from the mold, reducing the possible damage
to nano-scale patterns and improving separation speed. The stage
holding the substrate in the system may be capable of 6 axis motion
movements, therefore the substrate can move with its motion and
speed accurately controlled. The separation may include movements
of multiple steps with the speed and direction of each movement be
controlled. In one example, the substrate moves in both Roll and
Pitch motion, and at the same time moves down in Z: the combination
movement will peel the substrate from the mold diagonally. In
another example, the separation include 2 step movements: first the
substrate moves down in Z while going through Roll motion, then it
moves down in Z going through Pitch motion. Further, the separation
may be paused, waiting for the further propagation of separation
boundary.
[0141] The separation completion may be detected by sudden changing
of vacuum reading at the system and mold/substrate holders; it may
be detected by the recorded force during separation or a sudden
change of force reading; it may also be detected by processing the
camera images from top view of the die area during separation and
finding the time where the contact area disappeared.
[0142] When on die imprint is finished, the substrate stage will
move the substrate underneath the resist dispensing system if
dispensing resist is to be used. After dispensing, the stage will
move the substrate to the next position.
[0143] To improve the throughput of the system, resist droplets
with low evaporation rate may be used. All the resist droplets may
be dispensed at a time on all the dies of the substrate. Then the
substrate does not have to come back to dispenser station each time
for dispensing.
[0144] The improvements possessed by this disclosure are emphasized
again herein. The apparatus embodiments described in this
disclosure accomplish a full cycle of imprinting inside the chamber
through a process essentially involving deforming the mold and
positioning the substrate by the stage assembly. The speed to
finish each step of the process is primarily decided by stage
response and how fast to deform the mold. Using state-of-art stage
technology, stage response can be very fast and capable of
responding to requests of each step well within seconds.
Furthermore, the chamber uses vacuum to eliminate possibility of
trapping air between the mold and the substrate. The Z stage
required for the process is placed outside of chamber, which
significantly reduced the chamber volume, therefore reduced the
time for vacuum and pressure the chamber, increased the throughput.
The special ring seal design inside chamber allows the intrinsic
Air Cushion Press (ACP) of the process to be carried out for
nanoimprint. The ACP not only provides very uniform imprinting
force to achieve high pattern transfer fidelity, but also reduces
possible damage to the imprint molds and substrates, both are
crucial for manufacturing.
[0145] It is to be understood that the above described embodiments
are illustrative of only a few of the many embodiments that can
represent applications of this disclosure. Numerous and varied
other arrangements can be made by those skilled in the art without
departing from the spirit and scope of this disclosure.
[0146] When describing elements or features and/or embodiments
thereof, the articles "a", "an", "the", and "said" are intended to
mean that there are one or more of the elements or features. The
terms "comprising", "including", and "having" are intended to be
inclusive and mean that there may be additional elements or
features beyond those specifically described.
[0147] Those skilled in the art will recognize that various changes
can be made to the exemplary embodiments and implementations
described above without departing from the scope of the disclosure.
Accordingly, all matter contained in the above description or shown
in the accompanying drawings should be interpreted as illustrative
and not in a limiting sense.
[0148] It is further to be understood that the processes or steps
described herein are not to be construed as necessarily requiring
their performance in the particular order discussed or illustrated.
It is also to be understood that additional or alternative
processes or steps may be employed.
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