U.S. patent application number 11/943977 was filed with the patent office on 2008-07-10 for method and apparatus for rapid imprint lithography.
Invention is credited to Wei Zhang.
Application Number | 20080164638 11/943977 |
Document ID | / |
Family ID | 39593576 |
Filed Date | 2008-07-10 |
United States Patent
Application |
20080164638 |
Kind Code |
A1 |
Zhang; Wei |
July 10, 2008 |
METHOD AND APPARATUS FOR RAPID IMPRINT LITHOGRAPHY
Abstract
In accordance with the invention, a mold for imprinting a
patterned region by imprint lithography is provided with a
peripheral groove around the patterned region. The groove is
connected, as by channels through the mold, to a switchable source
for gas removal to prevent bubbles and for the application of
pressurized gas to separate the mold and substrate. In use, the
mold is disposed adjacent the moldable surface and gas is withdrawn
from the patterned region through the groove as the mold is pressed
toward and into the moldable surface. At or near the end of the
imprinting, the process is switched from removal of gas to the
application of pressurized gas. The pressurized gas passes through
the groove and separates or facilitates separation of the mold and
the moldable surface.
Inventors: |
Zhang; Wei; (Plainsboro,
NJ) |
Correspondence
Address: |
POLSTER, LIEDER, WOODRUFF & LUCCHESI
12412 POWERSCOURT DRIVE SUITE 200
ST. LOUIS
MO
63131-3615
US
|
Family ID: |
39593576 |
Appl. No.: |
11/943977 |
Filed: |
November 21, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60867515 |
Nov 28, 2006 |
|
|
|
Current U.S.
Class: |
264/500 ;
264/293; 425/385 |
Current CPC
Class: |
B82Y 40/00 20130101;
B29C 33/46 20130101; B29C 2059/023 20130101; B82Y 10/00 20130101;
B29C 2035/0827 20130101; B29C 37/0053 20130101; G03F 7/0002
20130101; B29C 33/10 20130101; B29C 37/006 20130101 |
Class at
Publication: |
264/500 ;
264/293; 425/385 |
International
Class: |
B29C 59/02 20060101
B29C059/02 |
Claims
1. A method of imprint lithography comprising the steps of:
providing a substrate having a moldable surface; providing a mold
having a molding surface for imprinting onto the moldable surface,
the molding surface substantially surrounded by a surface groove
for conducting fluid; disposing the mold adjacent the substrate
with the molding surface adjacent the moldable surface; pressing
the molding surface against the moldable surface to imprint the
moldable surface; hardening the moldable surface; and applying
pressurized fluid through the groove to facilitate separation of
the mold from the imprinted moldable surface.
2. The method of claim 1 further comprising the step of withdrawing
fluid through the surface groove prior to or during the
pressing.
3. The method of claim 1 wherein the pressing comprises sealing the
region between the molding surface and the moldable surface to
produce a sealed mold/substrate assembly and subjecting the
mold/substrate assembly to direct fluid pressure.
4. The method of claim 3 wherein the sealing comprises withdrawing
fluid through the surface groove.
5. The method of claim 1 wherein the pressing comprises pressing by
a mechanical press.
6. The method of claim 1 further comprising a step of moving apart
said substrate and said mold.
7. The method of claim 1 wherein said mold comprises a plurality of
voids to connect said surface groove at one end and the surface
opposite to said molding surface or the sidewall surface at the
other end.
8. The method of claim 7 wherein said voids provide fluid passage
to said surface groove.
9. The method of claim 1 wherein said surface groove is made by
either machining, or by a lithographical patterning and
etching.
10. The method of claim 1 wherein said mold comprises a plurality
of bodies bonded together.
11. Apparatus for imprinting a molding surface on a substrate
having a moldable surface comprising in operative relationship: a
mold having a molding surface, the molding surface substantially
surrounded by a surface groove for conducting fluid; a positioner
for placing the mold adjacent the substrate with the molding
surface adjacent the moldable surface; pressing apparatus for
pressing the mold against the substrate; and a source of
pressurized fluid switchably connected to introduce pressurized
fluid through the surface groove to facilitate separation of the
mold from the imprinted substrate.
12. The apparatus of claim 11 further comprising a controller to
control the sequence of imprinting the moldable surface and
introducing pressurized fluid into the groove to facilitate
separation of the mold from the imprinted moldable surface.
13. The apparatus of claim 11 further comprising a pump or a low
pressure reservoir switchably connected to the surface groove to
withdraw fluid through the groove.
14. The apparatus of claim 13 further comprises a controller to
control the sequence of withdrawing gas through the groove,
imprinting the moldable surface and introducing pressurized fluid
to facilitate separation of the mold from the imprinted
surface.
15. The apparatus of claim 11 wherein the mold further comprises a
plurality of through-holes connected to the surface groove.
16. The apparatus of claim 11 wherein the mold comprises a pattern
of projecting and recessed features for imprinting at least one
feature having a minimum lateral dimension of less than 200
nanometers.
17. The apparatus of claim 11 wherein the pressing apparatus
comprises a mechanical press.
18. The apparatus of claim 11 wherein the pressing apparatus
comprises a pressure vessel for enclosing the mold and substrate
and a source of pressurized fluid for introducing pressurized fluid
into the chamber.
19. The apparatus of claim 18 further comprising a controller to
control the sequence of introducing pressurized fluid into said
vessel to imprint the moldable surface and introducing pressurized
fluid into the groove to facilitate separation of the mold from the
imprinted moldable surface.
20. The apparatus of claim 18 further comprising a pump or a low
pressure fluid reservoir switchably connected to the surface groove
to withdraw fluid through the groove.
21. The apparatus of claim 20 further comprising a controller to
control the sequence of disposing the mold and substrate in the
pressure chamber, withdrawing fluid through the groove to seal the
region between the molding surface and the moldable surface,
introducing pressurized fluid into the chamber to imprint the
moldable surface, and introducing pressurized fluid into the
surface groove to facilitate separation of the mold and the
imprinted substrate.
22. The apparatus of claim 11 wherein said mold comprises a
plurality of voids to connect said surface groove at one end with
the surface opposite to said molding surface or the sidewall
surface at the other end.
23. The apparatus of claim 22 wherein said voids provide fluid
passage to said surface groove.
24. The apparatus of claim 11 wherein said surface groove is made
by either machining or by lithographic patterning and etching.
25. The apparatus of claim 11 wherein said mold comprises a
plurality of bodies bonded together.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application Ser. No. 60/867,515 of the same title filed by Wei
Zhang on Nov. 28, 2006 and which is incorporated herein by
reference.
FIELD OF THE INVENTION
[0002] This invention relates to methods and apparatus for
performing imprint lithography. It is particularly useful for
providing high resolution microscale or nanoscale imprint
lithography at high speed.
BACKGROUND OF THE INVENTION
[0003] Lithography is a key process in the fabrication of
semiconductor integrated circuits and many optical, magnetic,
biological and micromechanical devices. Lithography creates a
pattern on a thin film carried on a substrate so that, in
subsequent process steps, the pattern can be replicated in the
substrate or in another material that is added onto the
substrate.
[0004] Conventional lithography, referred to as photolithography,
involves applying a thin film of photosensitive resist to a
substrate, exposing the resist to a desired pattern of radiation
and developing the exposed resist to produce a physical pattern on
the substrate. Unfortunately, the resolution of patterns produced
by photolithography is limited by the wavelength of the exposing
radiation. Moreover, as pattern features become smaller,
increasingly expensive shorter wavelength equipment is
required.
[0005] Imprint lithography, based on a fundamentally different
principle, offers high resolution, high throughput, low cost and
the potential of large area coverage. In imprint lithography, a
mold with a pattern of projecting and recessed features is pressed
into a substrate-supported moldable surface such as a thin film of
polymer, deforming the shape of the film to form a relief pattern
in the film. After the mold is removed, the thin film can be
processed, as by removing reduced thickness portions of the film.
Such removal exposes the underlying substrate for further
processing such as etching, doping, or deposition. Imprint
lithography can be used to replicate patterns having high
resolution features in the microscale and nanoscale ranges. Details
of nanoscale imprint lithography ("nanoimprint lithography") are
described, for example, in U.S. Pat. No. 5,772,905 issued Jun. 30,
1998 and entitled "Nanoimprint Lithography". The '905 patent is
incorporated herein by reference.
[0006] A potential limitation on the rate of high speed
manufacturing using imprint lithography is the presence of gas
between the mold and the moldable film. Pressing the mold too
rapidly can entrap gas bubbles in tiny recessed regions,
deteriorating the resolution of the imprinted pattern. A second
limitation is the separation of the mold and the imprinted
substrate. Typically, after pressing, the mold and substrate are
mechanically separated from the edge by inserting a wedge between
the mold and substrate. This separation from the edge usually
requires that the mold and substrate be transported from the site
of the pressing apparatus to the site of the separation apparatus.
The separation step thus limits throughput of imprinting.
Furthermore, this conventional separation may cause cracking at the
edge of the mold or substrate. It thus, contributes to mold wear,
increases operating cost, and limits throughput.
[0007] Accordingly, it would be highly desirable to provide methods
and apparatus to permit more rapid pressing and separation in
imprint lithography.
BRIEF SUMMARY OF THE INVENTION
[0008] In accordance with the invention, a mold for imprinting a
patterned region by imprint lithography is provided with a
peripheral groove substantially around the patterned region. The
groove is connected, as by channels through the mold, to a
switchable fluid source for the application of pressurized fluid to
separate the mold and substrate. Advantageously, the same grooves
and channels may be used for gas removal to prevent bubbles.
[0009] In preferred use, the mold is disposed adjacent the moldable
surface and gas is withdrawn from the patterned region through the
groove and the channels as the mold is pressed toward and into the
moldable surface. After the mold contacts the moldable surface, gas
removal is either continued or stopped. At or near the end of the
imprinting, the process is switched from removal of gas to the
application of pressurized fluid such as gas. The pressurized fluid
passes through the channels and the groove, and it separates or
facilitates separation of the mold and the moldable surface.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0010] The advantages, nature and various additional features of
the invention will appear more fully upon consideration of the
illustrative embodiments now to be described in detail in
connection with the accompanying drawings. In the drawings:
[0011] FIG. 1 is a flow diagram of the steps involved in imprinting
a pattern in accordance with the invention;
[0012] FIGS. 2 and 3 are schematic cross sectional and elevational
views of a mold useful in the process of FIG. 1;
[0013] FIG. 4 schematically illustrates the molding apparatus at
various stages of the process of FIG. 1; and
[0014] FIGS. 5, 6 and 7 depict apparatus and results of an
experimental demonstration of the invention.
[0015] It is to be understood that the drawings are for purposes of
illustrating the concepts of the invention and are not to
scale.
DETAILED DESCRIPTION
[0016] Referring to the drawings, FIG. 1 is a flow diagram of the
steps involved in imprinting a pattern in accordance with the
invention. The first step shown in block A is to provide a
substrate having a moldable surface and a grooved mold having a
patterned region of projecting and recessed features for imprinting
a desired pattern.
[0017] The substrate having a moldable surface typically comprises
a substrate coated with a thin moldable layer such as a polymer
resist. The substrate can be any one of a wide variety of materials
such as semiconductors, polymers, dielectrics, and conductors. The
moldable layers can be coatings of polymers or layers of powdered
materials. A particularly advantageous coated substrate is
crystalline silicon or silicon dioxide coated with a thermal or UV
curable polymer. Exemplary combinations of substrate and resist are
set forth in the aforementioned '905 patent incorporated herein by
reference.
[0018] An exemplary grooved mold is schematically illustrated in
FIG. 2 (cross sectional view) and FIG. 3 (elevational view).
Referring to FIG. 2, the mold 200 typically comprises a
substantially planar surface that includes at least one pattern
region 200A to replicate a pattern by imprinting. The pattern
region is composed of projecting features 201A and recessed feature
201B that, upon pressing into a moldable surface, imprint a pattern
that has recessed features corresponding to mold projecting
features 201A and projecting features that correspond to mold
recessed features 201B. In highly advantageous applications, the
mold has a pattern of projecting and recessed features for
imprinting at least one feature having a minimum lateral dimension
of less than 200 nanometers.
[0019] The mold surface is provided with a grooved trench 202 on
the mold surface that includes pattern region 200A. The groove 202
is adjacent the pattern region 200A and preferably substantially
surrounds the pattern region. The groove 202 is in physical
communication with one or more through-holes 203 in the mold so
that fluid (e.g. gas) can be pumped from the groove 202 via the
through-hole(s) 203 from the mold/substrate interface.
Alternatively, the through-holes could be replaced by additional
surface channels to edges of the mold or in-body channels to
sidewalls of the mold (not shown). Such pumping minimizes entrapped
gas and facilitates molding. In addition fluid can be pumped into
the groove 202 after or near the end of imprinting to facilitate
release of the mold from the substrate. The fluid can be gas or
liquid. Typically it is air or inert gas.
[0020] The shape of the groove 202 around the pattern region is
advantageously in conformation with the outer periphery of the
pattern region 200A so that the groove 202 is closely adjacent the
boundary of the pattern region. Preferably the minimum distance
between the groove and the pattern boundary is about 0.5 millimeter
to 2.0 millimeter. Typical groove shapes are circular, or polygonal
(e.g. rectangular) to surround individual pattern regions. However
the groove shape can be zigzag to partially surround each of a
plurality of pattern regions. The depth of the groove 202 is
preferably in the range from about 1.0 micrometer to about 2.0
millimeters, although groove depth can range from about 50
nanometers to about one centimeter depending on the thickness of
the mold. The groove can have any of a wide variety of cross
sectional shapes. Typical cross sections can be squares,
rectangles, triangles, semi-circles and parallelograms. The
through-holes can be any desired cross section, but circular cross
sections are typical. The groove effective diameters are typically
in the range from about 5 micrometers to about 10 millimeters. At
least one through-hole connected to the groove is preferred.
Multiple through-holes connected to the groove are even more
preferable for even flow of gas or fluid.
[0021] The mold 200 is advantageously fabricated of quartz, fused
silica, metal semiconductor, polymer or a combination of these
materials. The mold body thickness should provide sufficient
mechanical strength for molding after the grooved trench and
through-holes are made. Typically, body thickness is about 2
millimeters or greater. The pattern region 200A can be made by any
of a wide variety of techniques depending on minimum feature size.
For patterns that include nanoscale minimum features, the pattern
region can be made by electron beam lithography. The groove trench
and through-holes can be made by conventional techniques including
machining (mechanical, laser, ultrasonic or jet), lithographic
patterning and etching (wet chemical or dry plasma) or a
combination of these techniques. The mold can be a homogenous body
or multilayer of various materials. Also, the mold can be made by
bonding several bodies together.
[0022] Referring to Block B of FIG. 1, after the mold and substrate
are provided, the next step is to dispose the mold adjacent the
substrate.
[0023] FIG. 4A illustrates the mold 400 disposed adjacent the
substrate 401 with the pattern 405 in position for imprinting the
moldable surface 402. The mold is positioned so that the groove 403
is adjacent the moldable surface of substrate 401. The mold and
substrate can be disposed in air or in a low pressure gas
ambient.
[0024] The third step (referring to Block C of FIG. 1) is to press
together the molding surface of the mold and the moldable surface
of the substrate and, during at least a portion of the pressing, to
remove gas through the groove and the through-holes.
[0025] FIG. 4B shows the mold 400 and substrate 401 pressed
together with the pattern region of projecting and recessed
features pressing against the moldable surface. The arrows pointing
outward from through-holes 404 indicate gas removal from the
mold/substrate interface through the groove 403 and the
through-holes 404. While some gas will be passively removed by the
reduction in volume as the mold and substrate are pressed together,
it is preferred to actively pump gas out through the groove and
through-holes. Active removal is effected by attaching the
through-holes to a low-pressure reservoir (not shown) or a gas pump
(not shown). Gas will flow from the region between the mold and the
substrate to a lower pressure region connected to the
through-holes.
[0026] Gas removal can be initiated prior to the start of the
pressing step or after the start of pressing. The gas removal
should begin early enough to remove gas between the pattern region
and the moldable layer before the pattern region seals against the
moldable layer.
[0027] The pressing can be affected in a variety of ways. One
approach is to press the mold and the substrate together by a high
precision mechanical press. For further details see U.S. Pat. No.
5,772,905.
[0028] Another approach is pressing by fluid pressure. The
interface between the mold and the substrate is sealed from
pressurized fluid, such as compressed air or inert gas that presses
the mold and substrate together. For further details see U.S. Pat.
No. 6,482,742, which is incorporated herein by reference. In this
mode of pressing, the withdrawal of gas prior to pressing can not
only assist in preventing bubbles but also can remove ambient gas
diffused into interface region to increase the pressure difference
between the interface region and the ambient. The withdrawal of gas
creates a pressure difference between the interface region and the
ambient. When the ambient pressure is increased, the pressure
difference is increased sufficiently high to seal the interface.
The withdrawal, thus, helps to seal the interface. Pressurized
fluid can be introduced around the sealed mold/substrate assembly
to imprint the patterned region into the moldable surface. The
process can achieve sealing without using a flexible film to seal
the interface, and, can be automatically sequenced for rapid
manufacturing. Other approaches to pressing include pressing driven
by the application of electrostatic or magnetic force.
[0029] The next step is to permit the moldable surface to harden
sufficiently to retain the imprinted pattern (referring to Block D
of FIG. 1). During the imprinting, the molding surface is
sufficiently sealed against the moldable surface that no
appreciable additional gas is withdrawn. This condition is
illustrated in FIG. 4C. The moldable surface, typically resist,
fully fills the space between the mold and the substrate. The
resist is hardened, as by UV or thermal curing, or cooling a
thermoplastic below its plastic transition temperature. The
substrate and the mold may be held together by the hardened resist.
The imprinting pressure can be removed before hardening or be
maintained during hardening.
[0030] The fifth step (referring to Block E of FIG. 1) is to
separate the mold from the substrate. This separation can be
achieved or assisted by the application of pressurized fluid
through the through-holes and the groove into the mold/substrate
interface. The inwardly directed arrows in FIG. 4D represent
pressurized fluid passing into the through-holes and the groove to
the mold/substrate interface. The fluid here can be gas or liquid.
The pressurized fluid first builds up at the groove region, and
then at the interface region to separate the mold from the molded
surface on the substrate.
[0031] The substrate and mold can then be moved apart. An
advantageous optional enhancement of the separation step is to
provide the substrate with a support having one or more vacuum
attachment regions 40B. The evacuation of regions 40B through
vacuum grooves (not shown) on body 403 can secure the substrate
when the substrate is lifted off as shown in FIG. 4E. The injection
of pressurized fluid into the interface and the application of
vacuum to retain the substrate can be automatically sequenced. Thus
each step in the imprinting process can be automatically controlled
and sequenced for high speed manufacture. A mold that has a blank
(smooth, flat) molding surface without surface replication features
can be used to planarize a polymer layer to avoid unwanted surface
variation of the substrate.
[0032] The invention may now be more clearly understood by
consideration of the following experiment performed to demonstrate
the workability of the method. FIG. 5 shows an enlarged view of the
mold used for the experiment. The body 500 of the mold is
approximately 1.5 inch.times.1.5 inch, 0.25 inch thick and is made
of quartz. The mold includes a circular grooved trench 501 and two
through-holes 502. The grooved trench has outer diameter of about
25 millimeters, a trench width of about 1 millimeter and a trench
depth of about 1 millimeter. The two through-holes 502 directly
connect to the grooved trench 501. The molding surface has surface
replication features 503 in sizes ranging from several micrometers
to several millimeters. The surface replication 2
[0033] FIG. 6a is a photo showing the testing setup with which the
experiment was performed. The testing setup consists of gas/vacuum
control 601, a base plate 602, a top plate 603 and a user interface
computer control panel (not shown). The computer control panel
controls the supplies of gas and vacuum pumping. However, the
process tested was controlled mainly by the manual valves 601.
[0034] FIG. 6b shows the mold 604 and bottom plate 605 of the
testing setup. The vacuum grooves to hold the mold against the
bottom plate can be seen through body of the mold. There are two
holes 606 through the bottom plate surrounded by two circular
grooves respectively. The two holes on the bottom plate are the two
through-holes.
[0035] Referring to FIG. 6c, the substrate 608 used in the
experiment was put on top of the mold with surface to be imprinted
contacting with top surface of the mold. In a commercial
embodiment, this placement could be done by a conventional
positioner. A UV curable resist layer was coated on the surface of
the substrate. The top plate with O-ring 607 is also shown at the
right of the photo. When the top plate was installed on the top of
the mold, the recessed area of the top plate formed a sealed
chamber. The substrate was cut from a Silicon wafer to fit into the
chamber and to cover the grooved trench of the mold.
[0036] FIG. 6d depicts the installed setup ready for testing.
Connector 609 goes to the sealed chamber. Connectors 610 go to the
through-holes of the bottom of the plate, then to the through-holes
of the mold and finally to the grooved trench of the mold.
Connector 611 goes to the vacuum grooves on the surface of the
bottom plate that holds the mold against the bottom plate. Screws
hold the sealed chamber for vacuuming and pressurizing.
[0037] The experimental process was as follows: (1) load the mold
on the bottom plate and turn on the vacuum to hold the mold; (2)
coat the UV curable layer on top of the substrate; (3) load the
coated substrate on the mold; (4) install the top plate on top of
the mold and clamp the sealed chamber with screws; (5) turn on
vacuuming inside the chamber and vacuuming through the grooved
trench; (6) turn off the vacuuming inside the chamber and maintain
vacuuming through the grooved trench; (7) fill pressurized nitrogen
into the chamber; (8) hold for a time period; (9) cure the UV
curable layer by UV exposure through the transparent body of the
mold; (10) release the pressure inside the chamber and take off the
top plate. The vacuuming through the grooved trench could be turned
off anytime after step 7; (11) flow pressurized nitrogen through
the grooved trench; (12) separate the substrate from the mold by
the blowing gas.
[0038] In ten runs the substrates were separated from the mold with
the inlet pressure of blowing nitrogen set at or gradually
increased to approximate 30 psi. The surface replication features
enclosed by the grooved trench were replicated into the UV cured
layer on all runs.
[0039] FIG. 7 shows a typical result of imprinting from the
experiment. Image 700 is the substrate with the trace of the
grooved trench 701 and surface patterns replicated from the mold.
The trace of the grooved trench is a closed loop indicating a good
seal for the imprint. The patterns were replicated uniformly
although variation of colors around a particle on the substrate was
seen. Image 702 shows imprinted patterns on the substrate near the
edges of the grooved trench 704, 705. On the image, patterns with
good imprinting quality were obtained right to the inner edge of
the grooved trench 704. Image 703 shows the imprinted pattern close
to the center of the substrate. The imprinting quality of the
patterns is very good.
[0040] It can now be seen that one aspect of the invention is a
method of imprinting a substrate having a moldable surface. It
comprises providing the substrate and providing a mold having a
molding surface for imprinting onto the moldable surface. The
molding surface is substantially surrounded by a surface groove for
conducting fluid. The mold is disposed adjacent the substrate with
molding surface adjacent the moldable surface. The molding surface
is pressed against the moldable surface to imprint the moldable
surface. Prior to and/or during the pressing, gas is advantageously
withdrawn through the surface groove. The moldable surface is
hardened to retain the imprint, and pressurized fluid is then
applied through the groove to facilitate separation of the mold
from the imprinted moldable surface.
[0041] Another aspect of the invention is apparatus for imprinting
a molding surface on a substrate having a moldable surface. The
apparatus including, in operative relation, a mold having a molding
surface that is substantially surrounded by a surface groove for
conducting fluid. A positioner can be provided to dispose the mold
adjacent the substrate with the molding surface adjacent the
moldable surface.
[0042] The apparatus can include a pump or low-pressure gas
reservoir switchably connected to withdraw gas through the surface
groove. It includes a source of pressurized fluid switchably
connected to apply pressurized fluid through the surface
groove.
[0043] Apparatus is provided to press the mold against the
substrate, and a controller is provided to direct the introduction
of pressurized fluid to separate the mold and the substrate. The
controller may advantageously also direct the withdrawal of gas
before and/or during pressing.
[0044] It is to be understood that the above-described embodiments
are illustrative of only a few of the many possible specific
embodiments which can represent applications of the invention.
Numerous and varied other arrangements can be made by those skilled
in the art without departing from the spirit and scope of the
invention.
* * * * *