U.S. patent application number 12/777623 was filed with the patent office on 2010-09-02 for reusable template for creation of thin films; method of making and using template; and thin films produced from template.
This patent application is currently assigned to PROTOCHIPS, INC.. Invention is credited to John Damiano, JR., Stephen E. Mick, David P. Nackashi.
Application Number | 20100221488 12/777623 |
Document ID | / |
Family ID | 37522772 |
Filed Date | 2010-09-02 |
United States Patent
Application |
20100221488 |
Kind Code |
A1 |
Mick; Stephen E. ; et
al. |
September 2, 2010 |
REUSABLE TEMPLATE FOR CREATION OF THIN FILMS; METHOD OF MAKING AND
USING TEMPLATE; AND THIN FILMS PRODUCED FROM TEMPLATE
Abstract
The present invention is directed generally to templates used in
the creation of thin-film replicas, for example, the creation of
thin films, such as carbon films, for use as specimen support in
electron-beam specimen analysis. More specifically, the present
invention is directed to novel reusable patterned templates, the
methodology of making these reusable templates, the templates made
from such methodologies, the use and reuse of these templates to
make thin films of any type for any purpose, and the thin films
made from these templates. A feature of the novel template of the
present invention is in its employment of one or more zones of
discontinuity, or undercuts, associated with the patterns
transferred into the template to allow for the removal of the thin
film from the template without sacrificing the structural integrity
of the template to prevent at least one re-use of the template.
Inventors: |
Mick; Stephen E.; (Apex,
NC) ; Damiano, JR.; John; (Apex, NC) ;
Nackashi; David P.; (Raleigh, NC) |
Correspondence
Address: |
MOORE & VAN ALLEN PLLC
P.O. BOX 13706
Research Triangle Park
NC
27709
US
|
Assignee: |
PROTOCHIPS, INC.
Raleigh
NC
|
Family ID: |
37522772 |
Appl. No.: |
12/777623 |
Filed: |
May 11, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11150382 |
Jun 10, 2005 |
7713053 |
|
|
12777623 |
|
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|
Current U.S.
Class: |
428/138 ;
264/241; 428/131 |
Current CPC
Class: |
Y10T 428/24331 20150115;
H01J 37/20 20130101; Y10T 428/24273 20150115; H01J 2237/2007
20130101 |
Class at
Publication: |
428/138 ;
428/131; 264/241 |
International
Class: |
B32B 3/10 20060101
B32B003/10; B29C 59/02 20060101 B29C059/02 |
Claims
1. A reusable template for use in creating thin films comprising:
(a) a base structure having a top surface, a bottom surface and a
thickness defined as the distance between the top surface and the
bottom surface; (b) one or more patterns in the top surface of the
base; said one or more patterns each having a respective aperture,
said respective aperture for each of said respective patterns
having a desired aperture shape defining a desired perimeter
boundary at the top surface of the base; and (c) one or more
cavities extending from said one or more aperture perimeter
boundaries into the thickness of the base structure, said one or
more cavities having a shape defined by one or more internal wall
surfaces extending into the thickness of the base; said one or more
cavities having a region of discontinuity between said one or more
cavities and their respective one or more aperture perimeter
boundaries.
2. (canceled)
3. The reusable template of claim 1 wherein said plurality of
patterns are arranged in a regular array of aperture shapes.
4. The reusable template of claim 3 wherein the base is an
amorphous substrate material.
5. The reusable template of claim 1 wherein the base is comprised
of crystalline material.
6. (canceled)
7. The reusable template of claim 1 wherein the base further
comprises a multilayered structure having a surface layer comprised
of a surface layer material and a substrate layer comprised of a
substrate layer material, said surface layer having a topside and
an underside, said surface layer underside being in contact with
said subsurface layer, said surface layer containing said one or
more apertures, said subsurface layer containing said one or more
cavities, said one or more cavities having a region of
discontinuity between said one or more cavities and said surface
layer apertures.
8. The reusable template of claim 7 wherein said region of
discontinuity comprises an undercut.
9. The reusable template of claim 8 wherein said undercut comprises
a region of the cavity walls proximate the aperture perimeter
boundary where such walls have a substantially retrograde
slope.
10. The reusable template of claim 8 wherein said undercut
comprises a region of the surface layer forming a lip at the
aperture perimeter boundary, said lip comprising a topside face, an
underside face substantially underneath said topside face, and a
depth, said underside face having an outer boundary, and an inner
boundary said lip underside face having length defined as the
distance between said outer and inner boundaries, said lip
underside face inner boundary contacting said cavity substrate
layer.
11. The reusable template of claim 10 wherein said lip underside
face inner boundary contacts said cavity substrate layer in a
region where said cavity walls have a substantially retrograde
slope.
12. The reusable template of claim 10 wherein said lip underside
face inner boundary contacts said cavity substrate layer in a
region where said cavity walls have a substantially re-entrant
slope.
13. A method of manufacturing reusable thin film templates
comprising the steps of: (a) creating a thin film template
workpiece having one or more layers of desired composition, said
workpiece having a top surface, a bottom surface and a depth; (b)
transferring patterned features from a pattern master into the
surface of the template workpiece to create one or more patterned
apertures having a desired aperture shape defining a desired
perimeter boundary in the top surface of the workpiece; and (c)
creating one or more cavities extending from said one or more
aperture perimeter boundaries into the thickness of the workpiece,
said one or more cavities having a shape defined by one or more
internal wall surfaces extending into the thickness of the base;
said one or more cavities having a region of discontinuity between
said one or more cavities and their respective one or more aperture
perimeter boundaries.
14. The method of claim 13 wherein the step of creating a workpiece
comprises creating a multilayered structure having a surface layer
comprised of a surface layer material and a substrate layer
comprised of a substrate layer material, said surface layer having
a topside and an underside, said surface layer underside being in
contact with said subsurface layer, said surface layer containing
said one or more apertures, said subsurface layer containing said
one or more cavities, said one or more cavities having a region of
discontinuity between said one or more cavities and said surface
layer apertures.
15. The method of claim 14 wherein said region of discontinuity
comprises an undercut.
16. The method of claim 15 wherein said undercut comprises a region
of the cavity walls proximate the aperture perimeter boundary where
such walls have a substantially retrograde slope.
17. The method of clam 15 wherein said undercut comprises a region
of the surface layer forming a lip at the aperture perimeter
boundary, said lip comprising a topside face, an underside face
substantially underneath said topside face, and a depth, said
underside face having an outer boundary, and an inner boundary said
lip underside face having length defined as the distance between
said outer and inner boundaries, said lip underside face inner
boundary contacting said cavity substrate layer.
18. The method of claim 17 wherein said lip underside face inner
boundary contacts said cavity substrate layer in a region where
said cavity walls have a substantially retrograde slope.
19. The method of claim 17 wherein said lip underside face inner
boundary contacts said cavity substrate layer in a region where
said cavity walls have a substantially re-entrant slope.
20-29. (canceled)
30. A method of manufacturing thin films comprising the steps of:
(a) coating a reusable thin film template with a release layer; (b)
applying the desired thin film to the release layer; and (c)
releasing the thin film from the release layer without sacrificing
the structural integrity of the thin film template such that the
thin film template remains available for at least one re-use; said
reusable thin film template comprising: a base structure having a
top surface, a bottom surface and a thickness defined as the
distance between the top surface and the bottom surface; one or
more patterns in the top surface of the base; said one or more
patterns each having a respective aperture, said respective
aperture for each of said respective patterns having a desired
aperture shape defining a desired perimeter boundary at the top
surface of the base; and one or more cavities extending from said
one or more aperture perimeter boundaries into the thickness of the
base structure, said one or more cavities having a shape defined by
one or more internal wall surfaces extending into the thickness of
the base; said one or more cavities having a region of
discontinuity between said one or more cavities and their
respective one or more aperture perimeter boundaries.
31-37. (canceled)
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not Applicable.
BACKGROUND OF THE INVENTION
[0003] The present invention is directed generally to templates
used in the creation of thin-film replicas, for example, the
creation of thin films, such as carbon films, for use as specimen
support in electron-beam specimen analysis. More specifically, the
present invention is directed to novel reusable templates, the
methodology of making these reusable templates, the templates made
from such methodologies, the use and reuse of these templates to
make thin films of any type for any purpose, and the thin films
made from these templates.
[0004] Several issued U.S. patents provide a background for
structures and methods of making replicas. For example, U.S. Pat.
No. 2,347,965 to Ramberg discloses a method to make a replica of
the surface of an opaque specimen through a two-step positive
replication process for examination with a transmission electron
microscope. In the disclosed process a specimen is first coated
with a thick amount of metal. The thick metal coating is
mechanically stripped from the specimen and coated with a thin
replicating material. The replica is completed by chemically
dissolving the metal to leave only the thin replicating material.
Thus, the negative metal replica of the specimen surface is
destroyed and can be used to create only one positive replica.
[0005] U.S. Pat. No. 2,572,497 to Law discloses a method to make a
positive silica replica of a copper mesh. In this patent, a copper
mesh serves as a template for creating a silica mesh. As the
process is described, the silica mesh is completed by etching away
the underlying copper mesh. The copper mesh template is destroyed
in the manufacture of the silica replica and can therefore only be
used one time.
[0006] U.S. Pat. No. 2,875,341 to Nesh discloses a method for
making a replica of a metallic surface through a two-step positive
replication process. The process disclosed in the patent requires
that a metallic object to be replicated have the shape of the inner
edge of a ring or can be cut to have said shape. In the first step
of the replication process, a plastic replica of the metallic
surface is made whereby plastic is applied to the metallic surface,
and as the plastic dries, it shrinks and separates itself from the
metallic surface. The plastic mold of the surface is then
evaporated with silica and possibly other masking materials.
Finally, the plastic is dissolved from the silica replica with
solvents. Accordingly each plastic mold from the surface can be
used to create only one replica.
[0007] U.S. Pat. No. 4,250,127 to Warren, et al., discloses a
method to make a specimen support grid for x-ray analysis as a
negative replica from a mold etched into a surface. The grid
disclosed in this patent is created by casting a carbon material
into a mold and etching away the mold once the casting is
completed. Thus the mold (or template) disclosed in this patent is
destroyed as a consequence of the process for making the grid.
[0008] U.S. Pat. No. 5,004,920 to Lee, et al. discloses a method to
collect asbestos from a sample of air. In the disclosed process, a
volume of air containing an asbestos sample to be collected is
passed through a filter. The filter with the collected sample is
affixed to a glass slide, coated with carbon both to form a
negative replica of the surface and to trap the asbestos specimen,
and then cut into small sections. The negative replica is completed
by submersing a small section in solvent to dissolve the filter and
thereby release the replica with embedded asbestos.
[0009] U.S. Pat. No. 6,645,744 to Ermantraut, et al., discloses a
bath used to selectively etch layers of a microstructure wherein
the bath consists of at least one biogenic agent. U.S. Pat. No.
6,821,692 also to Ermantraut, et al., discloses a method to create
a self-supported novolac (i.e. photoresist) structure by the
process of depositing, patterning, and releasing the structure from
a substrate. See also, Ermantraut, E; Wolfhart, K; and Tichelaar,
W, "Perforated support foils with pre-defined hole size, shape and
arrangement," Ultramicroscopy 74 (1998), pp 75-81 describing the
usage of the technology described in these two patent references.
Perforated support foils with holes of pre-defined size, shape and
arrangement and with hole sizes down to the sub-micrometer range,
named Quantifoil.RTM., are presented. The foils are fabricated
using semiconductor lithographic techniques. A sacrificial layer
that consists of a biopolymer, i.e. glutaraldehyde cross-linked
gelatin, is used. This layer is removed by proteinase treatment,
thus introducing an enzymatic reaction as a tool in microsystems
technology. The foils are particularly beneficial in electron
microscopy, when a specimen support is required with holes smaller
than those attainable with metal grids (.about.10 .mu.m). Foils
with a specific hole size and arrangement permit a further
automation of electron microscopic (EM) data acquisition
procedures.
[0010] Additionally, Downing, K, "Support Films with Uniform Hole
Size," Microscopy Today, 11(5), p. 54, 2003 describes a method for
producing a uniform distribution of holes that are all of the same
size in holey carbon films mounted on standard EM grids used as
specimen supports in electron cryo-microscopy. The resulting grids
are described as being a very effective intermediate between holey
films made with the various solvent techniques, which produce
random hole sizes, and commercial Quantifoil.RTM. grids, which have
uniform holes on a regular lattice.
[0011] However, the current state-of-the-art does not provide a
template structure that allows for a positive replica to be created
in a single step while preserving the template for reuse (i.e., the
template is not sacrificed, destroyed or otherwise damaged during
the removal of the replica). Moreover the prior art templates do
not allow for precise control over the thickness and type of
material used to form the replica. Nor can the prior art templates
can be custom created to have features for replication down to the
nanometer scale where the features can be precisely manufactured
and transferred into the replica as a pattern of any complexity.
Further, the there exists a need for the formation of thin film
replicas from a template that can be accomplished on a large scale
not requiring the template to but cut into small sections.
BRIEF SUMMARY OF THE INVENTION
[0012] The present invention addresses the need mentioned above by
providing a template structure that allows for a positive replica
to be created in a single step while preserving the template for
reuse. The present invention also allows for precise control over
the thickness and type of material used to form the replica. The
novel templates of the present invention described herein can be
custom created to have features for replication down to the
nanometer scale where the features can be precisely manufactured
and transferred into the replica as a pattern of any complexity.
Further, the present invention provides for the formation of thin
film replicas from the novel template that can be accomplished on a
large scale not requiring the template to be cut into small
sections. The present invention provides novel undercut profiles in
the template to cause a discontinuity to exist in any thin film
that is deposited upon the template structure thereby allowing the
surface features to be replicated in the thin film. Moreover, the
discontinuity in the deposited film resulting from the undercut
profile provides a mechanism for a solution to dissolve a release
layer that is deposited between the surface material and a
subsequently deposited thin film layer.
[0013] In a preferred embodiment of the present invention, there is
described a reusable template for use in creating thin films
comprising a base structure having a top surface, a bottom surface
and a thickness defined as the distance between the top surface and
the bottom surface; one or more patterns in the top surface of the
base; and one or more cavities extending from the aperture
perimeter boundaries into the thickness of the base structure. The
patterns each have a respective aperture having a desired aperture
shape defining a desired perimeter boundary at the top surface of
the base. The cavities have a shape defined by one or more internal
wall surfaces extending into the thickness of the base and have a
region of discontinuity between said one or more cavities and their
respective one or more aperture perimeter boundaries. In a
preferred embodiment, the plurality of patterns being oriented in
spaced relationship with one another and/or in a regular array of
aperture shapes.
[0014] The composition of the base could be any advantageous
material, such as an amorphous substrate material, a crystalline
material, such as for example, silicon, or other lattice structured
material. The base could be comprised of multiple layers in
stacked-up orientation to increase manufacturing yield. In a
preferred embodiment, the base further comprises a multilayered
structure having a surface layer comprised of a surface layer
material and a substrate layer comprised of a substrate layer
material. In a preferred embodiment, the surface layer has a
topside and an underside, the surface layer underside being in
contact with the subsurface layer. The surface layer contains these
apertures and the subsurface layer contains the cavities, these
cavities having a region of discontinuity between themselves and
the surface layer apertures. The region of discontinuity preferably
comprises an undercut.
[0015] The undercut can comprise a region of the cavity walls
proximate the aperture perimeter boundary where such walls have a
substantially retrograde slope. The undercut can also comprise a
region of the surface layer forming a lip at the aperture perimeter
boundary, the lip comprising a topside face, an underside face
substantially underneath the topside face, and a depth, the
underside face having an outer boundary, and an inner boundary. The
lip underside face has a length defined as the distance between the
outer and inner boundaries, the lip underside face inner boundary
contacting the cavity substrate layer. The lip underside face inner
boundary preferably contacts said cavity substrate layer in a
region where said cavity walls have a substantially retrograde
slope. The lip underside face inner boundary also can contact the
cavity substrate layer in a region where the cavity walls have a
substantially re-entrant slope.
[0016] In yet another preferred embodiment of the present
invention, there is also described a preferred method of
manufacturing reusable thin film templates comprising the steps of:
creating a thin film template workpiece having one or more layers
of desired composition, said workpiece having a top surface, a
bottom surface and a depth; transferring patterned features from a
pattern master into the surface of the template workpiece to create
one or more patterned apertures having a desired aperture shape
defining a desired perimeter boundary in the top surface of the
workpiece; and creating one or more cavities (as described herein)
extending from said one or more aperture perimeter boundaries into
the thickness of the workpiece.
[0017] In a further preferred embodiment, there is disclosed a
method of manufacturing reusable thin film templates comprising the
steps of: creating a thin film template workpiece having one or
more layers of desired composition, the workpiece having a top
surface, a bottom surface and a depth; applying a photoresist layer
to the top surface of the workpiece; placing a photomask,
containing one or more desired array of patterned features,
proximate the surface of the photoresist layer; transferring the
patterned features of the photomask into the photoresist layer such
that the photoresist layer is now absent in the area of the
patterned features, thereby exposing the top surface of the
workpiece in the area of the patterned features; removing the
photomask from proximity with the workpiece; transferring the
patterned features into the surface of the template workpiece to
create one or more patterned apertures having a desired aperture
shape defining a desired perimeter boundary in the top surface of
the workpiece; and creating one or more cavities (as described
herein) extending from said one or more aperture perimeter
boundaries into the thickness of the workpiece. In another
embodiment, the photoresist layer is removed.
[0018] There is also described herein as a preferred embodiment, a
thin film template whenever obtained by the processes described
herein.
[0019] Additionally, as another preferred embodiment, there is
described a method of manufacturing thin films comprising the steps
of coating a reusable thin film templates as described herein with
a release layer; applying the desired thin film to the release
layer; and releasing the thin film from the release layer without
sacrificing the structural integrity of the thin film template such
that the thin film template remains available for at least one
re-use. The method of manufacturing thin films according to this
preferred embodiment can also include the additional step of
attaching the thin films so produced to an electron microscopy
sample grid. The releasing step preferably comprises exposing the
release layer to a material that selectively attacks the release
layer without substantially attacking the thin film layer. The
release layer may be comprised of one or more materials that are
deposited upon the template by vacuum deposition techniques. The
thin film layer may be comprised of one or more materials that are
deposited upon the release layer by vacuum deposition techniques.
This preferred methodology may be repeated using the same thin film
template. Also described herein is a preferred thin film product
made by these processes, including where the thin film further
comprisesing an electron microscope sample grid attached to the
thin film.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0020] FIG. 1a shows plan view of a thin film template workpiece
according to a step of the method of manufacturing a thin film
template according to a preferred embodiment of the present
invention.
[0021] FIG. 1b is a cross-sectional view of the thin film template
workpiece taken along line 1b-1b of FIG. 1a according to a step of
the method of manufacturing a thin film template according to a
preferred embodiment of the present invention.
[0022] FIG. 2a shows plan view of a thin film template workpiece
according to a step of the method of manufacturing a thin film
template according to a preferred embodiment of the present
invention.
[0023] FIG. 2b is a cross-sectional view of the thin film template
workpiece taken along line 2b-2b of FIG. 2a according to another
step of the method of manufacturing a thin film template according
to a preferred embodiment of the present invention.
[0024] FIG. 3a shows plan view of a thin film template workpiece
according to a step of the method of manufacturing a thin film
template according to a preferred embodiment of the present
invention.
[0025] FIG. 3b is a cross-sectional view of the thin film template
workpiece taken along line 3b-3b of FIG. 3a according to another
step of the method of manufacturing a thin film template according
to a preferred embodiment of the present invention.
[0026] FIG. 4a shows plan view, of the thin film template workpiece
taken according to a step of the method of manufacturing a thin
film template according to a preferred embodiment of the present
invention.
[0027] FIG. 4b is a cross-sectional view the thin film template
workpiece taken along line 4b-4b of FIG. 4a according to another
step of the method of manufacturing a thin film template according
to a preferred embodiment of the present invention.
[0028] FIG. 5a shows plan view of a thin film template workpiece
according to a step of the method of manufacturing a thin film
template according to a preferred embodiment of the present
invention.
[0029] FIG. 5b is a cross-sectional view of the thin film template
workpiece taken along line 5b-5b of FIG. 5a according to another
step of the method of manufacturing a thin film template according
to a preferred embodiment of the present invention.
[0030] FIG. 6a shows plan view of the thin film template workpiece
according to a step of the method of manufacturing a thin film
template according to a preferred embodiment of the present
invention.
[0031] FIG. 6b is a cross-sectional view of the thin film template
workpiece taken along line 6b-6b of FIG. 6a according to another
step of the method of manufacturing a thin film template according
to a preferred embodiment of the present invention.
[0032] FIG. 7a shows plan view of a thin film template workpiece
according to a step of the method of manufacturing a thin film
template according to a preferred embodiment of the present
invention.
[0033] FIG. 7b is a cross-sectional view of the thin film template
workpiece taken along line 7b-7b of FIG. 7a according to another
step of the method of manufacturing a thin film template having an
isotropic undercut profile according to a preferred embodiment of
the present invention.
[0034] FIG. 8a shows plan view of a novel thin film template
according to a preferred embodiment of the present invention.
[0035] FIG. 8b is a cross-sectional view of the novel thin film
template having an isotropic undercut profile according to a
preferred embodiment of the present invention taken along line
8b-8b of FIG. 8a.
[0036] FIG. 9a shows plan view of a thin film template workpiece
according to a step of the method of manufacturing a thin film
template according to a preferred embodiment of the present
invention.
[0037] FIG. 9b is a cross-sectional view of the thin film template
workpiece taken along line 9b-9b of FIG. 9a according to another
step of the method of manufacturing a thin film template according
to a preferred embodiment of the present invention.
[0038] FIG. 10a shows plan view of a novel thin film template
according to a preferred embodiment of the present invention.
[0039] FIG. 10b is a cross-sectional view of a novel thin film
template having a re-entrant cross-sectional undercut profile
according to a preferred embodiment of the present invention taken
along line 10b-10b of FIG. 10a.
[0040] FIG. 11a shows plan view of a novel thin film template
according to a preferred embodiment of the present invention.
[0041] FIG. 11b is a cross-sectional view of a novel thin film
template having a vertical cross-sectional undercut profile
according to a preferred embodiment of the present invention taken
along line 11b-11b of FIG. 11a.
[0042] FIG. 12a shows plan view of a novel thin film template
according to a preferred embodiment of the present invention.
[0043] FIG. 12b is a cross-sectional view of a novel thin film
template having a retrograde cross-sectional undercut profile
according to a preferred embodiment of the present invention taken
along line 12b-12b of FIG. 12a.
[0044] FIG. 13a shows plan view of a novel thin film template
according to a preferred embodiment of the present invention.
[0045] FIG. 13b is a cross-sectional view of a novel thin film
template having a complex retrograde and re-entrant cross-sectional
undercut profile according to a preferred embodiment of the present
invention taken along line 13b-13b of FIG. 13a.
[0046] FIG. 13c is an enlarged view of the area 13c in FIG.
13b.
[0047] FIG. 14a shows plan view of a novel thin film template
according to a preferred embodiment of the present invention.
[0048] FIG. 14b is a cross-sectional view of a novel thin film
template having a complex retrograde and re-entrant cross-sectional
undercut profile according to a preferred embodiment of the present
invention taken along line 14b-14b of FIG. 14a.
[0049] FIG. 15 describes a process of use of the novel thin film
template described herein and a method of creating thin films
according to a preferred embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0050] Referring to FIG. 1a, there is shown a plan view of a novel
thin film template workpiece 1 created according to a preferred
embodiment of the present invention. FIG. 1b is a cross-sectional
view of the workpiece 1 taken along lines 1b-1b of FIG. 1a. The
workpiece can be of any desired size and shape, but is shown here
in a substantially rectangular shape. In a preferred embodiment,
the template workpiece 1 initially comprises a substrate material
200 and a surface material 100, it being a generally preferred
strategy to have the substrate and surface materials ultimately
formed into an end product template according to the preferred
teachings of the present invention. As such, the term "workpiece"
as used herein is intended to generally refer to the collection of
materials or layers (e.g., substrate material 200, surface material
100, and other layers that may be employed, such as a photoresist
layer 300 (FIG. 2), photomask layer 400 (FIG. 4), and the like,
that are used in the creation of the template). The substrate
material 200 has a thickness 140, and a top surface 2. The
substrate material could comprise one material, such as for
example, silicon, or a combination of layers of materials of choice
(whether homogeneous, composite, multilayered, etc.). In one
preferred embodiment, the substrate material 200 can be silicon
having a crystalline orientation of (100), for example, a 4-inch
silicon (100) wafer. It will be understood and appreciated that
other starting materials, such as crystalline structures with
different crystalline orientations, wafer pieces, non-crystalline
materials, and substrates of different sizes and shapes can be
employed to advantage practicing the teachings of this
invention.
[0051] Taking this substrate 200, there is then deposited (or
grown, or otherwise coated or placed) onto its surface (preferably
only on the top surface 2, a surface material 100, having a
thickness 120, for example, a 200 nm thick low-stress silicon
nitride. The surface material 100 has a surface layer 4. The
workpiece at this stage now has a total thickness 160 equal to the
combined thickness of the substrate 200 and surface 100 layers.
Preferably, the total thickness 160 of the workpiece 1 is
sufficient to permit handling, or alternatively, to permit bonding
of the workpiece 1 onto a suitable handle (not shown). It will also
be appreciated and known to those of ordinary skill in the art that
that other surface materials, combinations of surface materials
(whether homogeneous, composite, multilayered, etc.), thicknesses
and shapes are possible and that the surface material as part of
the manufacturing process or as a matter of convenience may be
deposited (or grown, or otherwise coated or placed) on both the top
surface 2 and bottom surface 3 of the substrate 200. It is also a
possibility that material compositions may exist that already have
a multilayered structure that could be employed as the substrate,
surface, and/or as a combination substrate/surface material.
[0052] FIG. 2a shows plan view of a thin film template workpiece
according to a step of the method of manufacturing a thin film
template according to a preferred embodiment of the present
invention. FIG. 2b is a cross-sectional view of the thin film
template workpiece taken along line 2b-2b of FIG. 2a according to
another step of the method of manufacturing a thin film template
according to a preferred embodiment of the present invention.
Referring now to FIGS. 2a and 2b, once the desired substrate and
surface material template workpiece 1 is assembled, a next
preferred step is to apply a light-sensitive material, or
photoresist layer 300, having a desired thickness 180 onto the
surface 4 of the surface material 100. The use of photoresist
layers is known in the art of photolithography, and the thickness
180 of the photoresist layer 300 will vary depending on the
patterns that are to be created. In a preferred embodiment, the
photoresist layer 300 can be applied in many different ways, such
as the preferred spin coating techniques known in the art. Spray,
dip and other techniques of applying the photoresist layer are
known in the art, including, the further steps of oven baking or
other heat treatment (such as hot plate) of the applied photoresist
layer.
[0053] FIG. 3a shows plan view of a thin film template workpiece
according to a step of the method of manufacturing a thin film
template according to a preferred embodiment of the present
invention. FIG. 3b is a cross-sectional view of the thin film
template workpiece taken along line 3b-3b of FIG. 3a according to
another step of the method of manufacturing a thin film template
according to a preferred embodiment of the present invention.
Referring to FIGS. 3a and 3b, as a next preferred step, a photomask
400, such as, e.g., a contact photolithographic mask having a
surface 6, is placed into contact with the photoresist 300. The
photomask 400 is created to contain the desired array of patterns
or features 500 (e.g., an array of circular features) which are to
be transferred onto the template workpiece 1. The patterns 500 on
the photomask 400 can be of any desired configuration, including
configurations that will facilitate programming of the
instrumentation (e.g., equipment used in the manufacture of the
template and/or equipment that will employ the thin films made from
these templates). The creation of a photomask 400 is well known in
the art. The outer boundary of these patterns may sometimes be
referred to herein as an aperture, an opening and/or an aperture
perimeter boundary. As will be appreciated in the art, the aperture
or pattern shapes can be any desired shapes, sizes and dimensions.
Certain shapes may be better suited for certain thin film
applications. For example, shapes that would be of interest in this
technique would include those suitable for microfabrication (i.e.
features less than about 1 mm and pitches generally less than 1 mm
also). In terms of shapes, patterns comprised of conics, squares,
hexagonal arrays, etc. can all be of value in, e.g., the cryoTEM
community.
[0054] In a preferred embodiment, the photomask 400 is designed to
have an array of 2 .mu.m diameter 510 transparent circular features
500 on a 4 .mu.m pitch 530, 540 (as measured from the center 520 of
adjacent circular features 500). As can be seen, the features 500
in the photomask 400 define the footprint 310 or area of the
photoresist 300 to be removed in subsequent steps. The area of the
footprint 310 exposed through each feature 500 will be available
for, e.g., selective irradiation with, e.g., UV light or other
radiation source. In one embodiment, the features 500 are holes cut
out of the photomask 400. In another embodiment, the features 500
are non-opaque (transparent) regions in an otherwise opaque
photomask 400 such that the non-opaque (transparent) regions remain
vulnerable to UV or other radiation techniques. As can be
appreciated, the opaqueness regions 310 of the photomask can be
created in numerous ways known in the art. In an alternative
preferred embodiment, projection or other non-contact lithography
techniques as well as e-beam lithography, dip-pin lithography,
nano-imprinting techniques or other pattern transfer techniques
well known in the art could be used to advantage to transfer the
pattern of the photomask 400 or other pattern master into the
photoresist layer 300 of the template workpiece 1. Non-contact
lithography techniques are often employed where the topography of
the workpiece 1 is irregular, or where contact could damage the
substrate layer 200.
[0055] Additionally, there are many different techniques known in
the art or that will become known in the art for transferring of a
pattern. One well known general technique (with many variants)
includes, for example and without limitation, photolithography
(employing the combination of a photo definable polymer (i.e., a
photoresist) and a physical photomask technique. Another pattern
transfer technique could include, e.g., block copolymers are a
class of polymers that are *self-ordering* and that, can be used as
a pattern master to create the pattern in the surface layer, etc.
(i.e., the block copolymer serves the dual roles of photoresist and
photomask). E-beam lithography and dip-pen lithography are examples
of *maskless lithography* whereby a pattern is created directly in
a photoresist layer without a photomask. Nano-imprinting is a
technique used to *mechanically stamp* a master pattern (i.e.,
photomask in the form of a stamp) into a polymer layer. All of
these techniques could be used quiet readily to create the pattern
in the template of the present invention, it being the intent that
any such transfer technique known or later discovered could be
employed to advantage with the present invention.
[0056] FIG. 4a shows plan view of the thin film template workpiece
taken according to a step of the method of manufacturing a thin
film template according to a preferred embodiment of the present
invention. FIG. 4b is a cross-sectional view the thin film template
workpiece taken along line 4b-4b of FIG. 4a according to another
step of the method of manufacturing a thin film template according
to a preferred embodiment of the present invention. The masked,
photoresist layer of the workpiece 1 is now subjected to UV light
of an appropriate wavelength (or other suitable radiation) to
transfer the pattern of the photomask 400 into the photoresist
layer 300. Next, the pattern in the photoresist layer 300 is
developed using standard photolithographic development techniques.
As a result, the photoresist layer 300 is now developed or
patterned so that the surface material 100 is exposed in areas 110
where it is desired to remove the surface material 100. Preferably,
but not required, the photomask 400 is now removed.
[0057] Once the features 500 of FIGS. 3a and 3b have been
transferred through the photoresist layer 300, with respect to
FIGS. 4a and 4b the desired areas 110 of the surface layer 100 can
be further processed (removed) with, e.g., an etchant of desired
selectivity. The selection of an etchant(s) may depend on whether
one desires to etch through the surface layer 100 in the desired
areas 110 without substantially effecting the integrity of the
subsurface material 200 below such areas 110, or whether one
desires to etch through the surface layer 100 in the desired areas
110 and into a portion of the subsurface material 200 below such
areas 110. Referring now to FIG. 5a, there is shown a plan view of
a thin film template workpiece 1 according to a step of the method
of manufacturing a thin film template according to a preferred
embodiment of the present invention. FIG. 5b is a cross-sectional
view of the thin film template workpiece 1 taken along line 5b-5b
of FIG. 5a according to another step of the method of manufacturing
a thin film template according to a preferred embodiment of the
present invention. As a result, the surface layer area 110 is now
developed or patterned so that the substrate material 200 is
exposed in areas 210 where it is desired to remove the substrate
material 200.
[0058] FIG. 6a shows plan view of the thin film template workpiece
1 according to a step of the method of manufacturing a thin film
template according to a preferred embodiment of the present
invention. FIG. 6b is a cross-sectional view of the thin film
template workpiece 1 taken along line 6b-6b of FIG. 6a according to
another step of the method of manufacturing a thin film template
according to a preferred embodiment of the present invention.
Referring to FIGS. 5a, 5b, 6a and 6b there are illustrated two
preferred techniques for transferring the pattern into the surface
layer 100. For example, based on the composition of the surface
material 100 and/or the subsurface material 200, the transfer of
the pattern 500 may be focused solely on the surface layer 100
(FIG. 5b), so that the etchant used for the surface layer 100 does
not materially effect the subsurface material 200. For example,
where the surface layer 100 is silicon dioxide and the substrate
layer 200 is silicon, then the use of Hydrofluoric Acid will be
selectively specific in etching away the surface silicon dioxide
without materially effecting the silicon substrate layer. In
another embodiment, the transfer of the pattern 500 within the
aperture boundaries may be directed to both the surface layer 100
and the subsurface layer 200 in areas 220 such that the pattern is
transferred into the substrate layer 200 to a desired depth 230.
Additionally, it is possible, if desired, that portions of the
workpiece 1 be treated or processed (e.g., etched) differently than
other portions of the workpiece, so that, e.g., one layer may be
etched differently than another layer, or, e.g., certain features
500 may be processed differently from other features 500 on the
same workpiece 1.
[0059] For example, in a preferred embodiment, referring to FIGS.
6a and 6b, the transfer of the pattern from the photoresist layer
into the surface material can be achieved with a Reactive Ion Etch
("RIE") of a silicon nitride surface layer 100. However, in this
embodiment, the etchant can also preferably etch into a silicon
substrate layer 200 to a desired cavity depth 230. The depth of the
cavity created can vary, but could be on the order of 100 nm in the
case of a silicon wafer as noted above. Although the etch profile
indicated in the areas 220 of the substrate layer 200 are depicted
as being generally cylindrical in nature, depending on the
substrate material (and its, e.g., crystalline or other structure,
etc.) and the etchants used, the resulting etch profile (or cavity)
geometry could vary. Referring again to FIGS. 5a and 5b, the
etchant can be chosen to be highly selective to the surface
material 100 and less or not selective to the substrate material
200. As will be apparent in view of the teachings of this
invention, the substrate material(s) 200 and surface material(s)
100 and various etchants, etc. can be selected with a view towards
optimizing the relative selectivity of the various etchants to the
surface and substrate layers to create preferred templates
employing various undercut structures.
[0060] Referring now to FIG. 9a there is shown a plan view of a
thin film template workpiece 1 according to a step of the method of
manufacturing a thin film template according to a preferred
embodiment of the present invention. FIG. 9b shows a
cross-sectional view of the thin film template workpiece 1 taken
along line 9b-9b of FIG. 9a according to another step of the method
of manufacturing a thin film template according to a preferred
embodiment of the present invention. In a preferred embodiment, the
photoresist layer 300 is stripped away or otherwise removed
(although in an alternate embodiment, it is not necessary to strip
the photoresist layer) prior to further processing of the exposed
areas 220 of the substrate 200. The surface of the workpiece 1 can
then preferably be dipped in concentrated Hydrofluoric Acid (or
other suitable substance) to remove any native oxide that may have
formed on the exposed surface 220 of the silicon (or other
material) substrate layer 200.
[0061] Referring still to FIG. 9, a silicon subsurface layer 100
can preferably be further exposed to a potassium hydroxide (KOH)
etch at 60.degree. C. for 1 minute, followed by a deionized water
(Di H.sub.2O) rinse, followed by a methanol soak and then finally
air dried. The result of such etch is the final template. Creation
of a preferred undercut structure or profile 950 beneath the
surface material layer 100 can be accomplished in numerous final
template configurations such as those illustrated in, e.g., the
exemplary FIGS. 8, and 10-14. The varying undercut structure or
profile 950 configurations can be influenced by the selected
substrate material(s) and the etchant(s) used. Moreover, it will be
understood and appreciated that other etchant temperatures, etch
times, and chemicals for both soaking and rinsing the workpiece can
be employed to advantage practicing the teachings of this
invention.
[0062] For example, FIG. 7a shows plan view of a thin film template
workpiece according to a step of the method of manufacturing a thin
film template according to a preferred embodiment of the present
invention. FIG. 7b is a cross-sectional view of the thin film
template workpiece taken along line 7b-7b of FIG. 7a according to
another step of the method of manufacturing a thin film template
having an isotropic undercut profile 950 according to a preferred
embodiment of the present invention. To accomplish this isotropic
undercut profile, the workpiece 1 such as illustrated in FIG. 6b is
subjected to, e.g., one or more etching procedure(s) such as the
example described above in conjunction with the workpiece shown in
FIG. 9. As noted earlier, the etching step(s) can proceed with or
without the presence of the photoresist layer 300. During this
etching process, the etchant is selected to be selective to the
exposed substrate material layer 220, but not the surface material
layer 100. However, one could select an etchant that etches both
layers (100, 200) so that the earlier step of etching the surface
layer is integrated into the step of later etching the substrate
layer 200. It was found that during this etching step, it was
possible to etch away substrate material 200 from directly
underneath the surface material layer 100 proximate the radius 510
of the surface feature(s) or pattern(s) 500 to create a cavity
having an undercut profile, or lip, or zone of discontinuity 950
between the surface layer 100 and the substrate layer 200 that has
advantageous properties when the template is later used to create
thin films. The advantages of the undercut 950 include the ability
to easily remove the thin film layer (not shown) from the surface
layer 100, or in the case of FIG. 14b, the subsurface layer 200
without damaging or requiring the destruction or sacrificing of the
template.
[0063] Referring again to FIGS. 7a and 7b, there is illustrated one
possible embodiment of an isotropic etch technique resulting in a
substantially isotropic, or hemispherical cross-sectional profile
290 in the substrate material 200. In a preferred embodiment, the
undercut or region of discontinuity 950 has a width 250 sufficient
to create a discontinuity between the surface material layer 100
and the subsurface material layer 200. Typically, this width 250
will be greater than zero (except as illustrated in connection with
FIG. 14). As will be seen, the pattern is transferred into the
substrate 200 to a desired depth 240 and a new radial diameter 265
is created. Although the general shape of the etched pattern 290 is
illustrated here as a substantially hemispherical cavity shape, it
is understood that many different shapes can result (based on,
e.g., the substrate material and the etchants used) while still
creating an advantageous undercut 950. Various shapes (or variants
thereof) of the patterned area (cavity) of the substrate layer 200
could include, without limitation, hexagonal, octagonal, nonagonal,
decagonal, geodesic, hemispherical, substantially spherical, cubic,
square, rectangular, pyramidal, conical, frusto-conical, and any
other shape that may follow the lattice (crystalline or otherwise)
structure of the substrate layer(s) 200.
[0064] In a preferred embodiment, the surface layer has a topside
and an underside, the surface layer underside being in contact with
the subsurface layer. The surface layer contains one or more
apertures and the subsurface layer contains one or more cavities,
these cavities having a region of discontinuity between themselves
and the surface layer apertures or aperture perimeter boundaries.
The region of discontinuity preferably comprises an undercut. The
undercut can comprise a region of the cavity walls proximate the
aperture perimeter boundary where such walls have a substantially
retrograde slope. The undercut can also comprise a region of the
surface layer forming a lip at the aperture perimeter boundary, the
lip comprising a topside face, an underside face substantially
underneath the topside face, and a depth, the underside face having
an outer boundary, and an inner boundary. The lip underside face
has a length defined as the distance between the outer and inner
boundaries, the lip underside face inner boundary contacting the
cavity substrate layer. The lip underside face inner boundary
preferably contacts said cavity substrate layer in a region where
said cavity walls have a substantially retrograde slope. The lip
underside face inner boundary also can contact the cavity substrate
layer in a region where the cavity walls have a substantially
re-entrant slope.
[0065] Referring now to FIG. 8a, there is depicted a plan view of a
novel thin film template 111 made according to a preferred
embodiment of the present invention. FIG. 8b is a cross-sectional
view of the novel thin film template 111 having an isotropic
undercut profile according to a preferred embodiment of the present
invention taken along line 8b-8b of FIG. 8a. This figure
illustrates the result of the etching processes described in
connection with FIGS. 7a and 7b, except that in FIGS. 8a and 8b,
the photoresist layer 300 has now been removed. In this form, this
preferred thin film template 111 is now ready for use, and reuse,
in the creation of thin films (discussed later herein).
[0066] Similarly, FIG. 10a shows a plan view of a novel thin film
template 111 according to a preferred embodiment of the present
invention. FIG. 10b is a cross-sectional view of a novel thin film
template 111 having a re-entrant cross-sectional undercut profile
according to a preferred embodiment of the present invention taken
along line 10b-10b of FIG. 10a. In this particular embodiment, the
result of the etching procedures creates an anisotropic
cross-sectional profile 292 in the substrate material 200 in the
patterned areas having a desired depth 240. Although the general
shape of the etched pattern 292 is illustrated here as an
anisotropic shape, (here, essentially an inverted, flat-topped
pyramidal shape) it is understood that many different shapes of
varying degrees of geometric or non-geometric complexity can result
while still creating an advantageous undercut 950. In this
embodiment, the etching procedure creates an array of anisotropic
shapes having a first wall face 771 defined by a top edge 781,
bottom edge 782, and opposed side edges 785, 786; a second wall
face 774 adjacent the first, defined by a top edge 775, bottom edge
776, and opposed side edges 786, 783; a third wall face 772
opposite the first and adjacent the second, defined by a top edge
777, bottom edge 778, and opposed side edges 783, 784; a fourth
wall face 773 opposite the second and adjacent the first, defined
by a top edge 779, bottom edge 780, and opposed side edges 784,
785; and a base 770. The resulting undercut 950 has a desired width
250.
[0067] FIG. 11a shows plan view of a novel thin film template 111
according to a preferred embodiment of the present invention. FIG.
11b is a cross-sectional view of a novel thin film template 111
having a vertical cross-sectional undercut profile 950 according to
a preferred embodiment of the present invention taken along line
11b-11b of FIG. 11a. In this particular embodiment, the result of
the etching procedures creates an anisotropic cross-sectional
profile 294 in the substrate material 200 to a depth 240 in the
patterned areas. As will be seen, the undercut or lip 950 has a
width 250. Although the general shape of the etched pattern 292 is
illustrated here as an anisotropic shape, (here, essentially an
inverted, flat-topped pyramidal shape) it is understood that many
different shapes of varying degrees of geometric or non-geometric
complexity can result while still creating an advantageous undercut
950. In this embodiment, the etching procedure creates an array of
anisotropic shapes, substantially cubic shapes essentially defined
by four substantially vertical walls 281, 282, 283, 284 and a base
280.
[0068] FIG. 12a shows plan view of yet another novel thin film
template 111 according to a preferred embodiment of the present
invention. FIG. 12b is a cross-sectional view of a novel thin film
template 111 having a retrograde cross-sectional undercut profile
296 according to a preferred embodiment of the present invention
taken along line 12b-12b of FIG. 12a. This embodiment achieves a
pattern in the substrate that is somewhat of an inverted shape when
compared to the shape in FIGS. 10a and 10b. In this embodiment, the
etching procedure creates an array of anisotropic shapes having a
first retrograde wall face 622 defined by a top edge 606, bottom
edge 608, and opposed side edges 632, 630; a second retrograde wall
face 624 adjacent the first, defined by a top edge 602, bottom edge
604, and opposed side edges 632, 626; a third retrograde wall face
618 opposite the first and adjacent the second, defined by a top
edge 610, bottom edge 612, and opposed side edges 626, 628; a
fourth retrograde wall face 620 opposite the second and adjacent
the first, defined by a top edge 614, bottom edge 616, and opposed
side edges 628, 630; and a base 600. The resulting undercut 950 has
a desired width 250. Additionally, FIG. 12b illustrates that a
retrograde wall face will create a zone of additional, if no
independent, discontinuity owing to its retrograde slope occurring
over the retrograde distance 250a. The zone of discontinuity is
created by either the undercut region 295 and/or by the retrograde
slope of the wall faces 622, 624, 618 and/or 620. It is preferred
that the area of discontinuity around the openings, or apertures in
the surface layer created by the patterning 500 of the surface
layer be as great as possible, however, so long as some area of
discontinuity is created around these apertures, the benefits of
the invention can be enjoyed.
[0069] FIG. 13a shows plan view of a novel thin film template 111
according to a preferred embodiment of the present invention. FIG.
13b is a cross-sectional view of a novel thin film template 111
having a complex retrograde and re-entrant cross-sectional undercut
profile according to a preferred embodiment of the present
invention taken along line 13b-13b of FIG. 13a. FIG. 14a shows plan
view of a novel thin film template 111 according to a preferred
embodiment of the present invention. FIG. 14b is a cross-sectional
view of a novel thin film template 111 having a complex retrograde
and re-entrant cross-sectional undercut profile according to a
preferred embodiment of the present invention taken along line
14b-14b of FIG. 14a. Referring now to FIGS. 13a, 13b, 14a, and 14b,
there are disclosed preferred thin film templates 111 having
similar features, the primary differences being that a surface
layer 100 was not employed in the final template structure (111,
FIG. 14b), such surface layer either being absent the entire
manufacturing process, or removed during the manufacturing process.
In the embodiment shown in FIG. 14b, the undercut 950 is not
actually an undercut going under the surface layer 100 because in
this embodiment, the substrate layer 200 was the final remaining
layer, the "undercut" 950 here being represented by the inversely
declining (or retrograde) wall faces 801, 803, 805, 807 that create
a discontinuity at their respective upper edges 827, 812, 817,
822.
[0070] Referring still to FIGS. 13 and 14, each patterned area 210
in the substrate layer 200 has somewhat of a geodesic ball shape,
here with an upper, quasi-hemispherical section of the patterned
area within the substrate material 200 being defined by the
retrograde wall faces 801, 803, 805, 807, while a substantially
mirror-image, lower, quasi-hemispherical section of the patterned
area within the substrate material 200 being defined by the
respective adjoining re-entrant wall faces 802, 804, 806, 808, the
upper quasi-hemispherical section being similar to the profile
described in connection with FIG. 12.
[0071] For example, the upper quasi-hemispherical section of the
patterned substrate is defined by a first upper retrograde wall
face 801 defined by a top edge 827, bottom edge 826, and opposed
side edges 809, 824; a second upper retrograde wall face 803
adjacent the first, defined by a top edge 812, bottom edge 811, and
opposed side edges 809, 814; a third upper retrograde wall face 805
opposite the first and adjacent the second, defined by a top edge
817, bottom edge 816, and opposed side edges 814, 819; and a fourth
upper retrograde wall face 807 opposite the second and adjacent the
first, defined by a top edge 822, bottom edge 821, and opposed side
edges 819, 824; and a base 600. The resulting undercut 950 has a
desired width 250. First upper retrograde wall face 801 shares the
same side edge 809 with second upper retrograde wall face 803.
First upper retrograde wall face 801 shares its other side edge 824
with fourth upper retrograde wall face 807. Second upper retrograde
wall face 803 shares its other side edge 814 with third upper
retrograde wall face 805. Third upper retrograde wall face 805
shares its other side edge 819 with fourth upper retrograde wall
face 807.
[0072] Similarly, the lower quasi-hemispherical section of the
patterned substrate is defined by a first lower re-entrant wall
face 802 sharing as its top edge 826 the bottom edge 826 of first
upper retrograde wall face 801, bottom edge 828, and opposed side
edges 810, 825; a second lower re-entrant wall face 804 adjacent
the first, sharing as its top edge 811 the bottom edge 811 of the
second upper retrograde wall face 803, a bottom edge 813 and
opposed side edges 810, 815; a third lower re-entrant wall face 806
sharing as its top edge 816 the bottom edge 816 of third upper
retrograde wall face 805, bottom edge 818, and opposed side edges
815, 820; and a fourth lower re-entrant wall face 808 sharing as
its top edge 821 the bottom edge 821 of fourth upper retrograde
wall face 807, bottom edge 823, and opposed side edges 825, 820;
and a base 800. The resulting undercut 950 has a desired width 250.
First lower re-entrant wall face 802 shares the same side edge 810
with second lower re-entrant wall face 804. First lower re-entrant
wall face 802 shares its other side edge 825 with fourth lower
re-entrant wall face 808. Second lower re-entrant wall face 804
shares its other side edge 815 with third lower re-entrant wall
face 806. Third lower re-entrant wall face 806 shares its other
side edge 820 with fourth lower re-entrant wall face 808.
[0073] As will be appreciated from the teachings herein, the angles
of the sidewalls formed in the patterned subsurface area 210 below
the surface layer 100 can range from retrograde to fully vertical
to re-entrant. In the case of the template 111 not employing a
surface layer (such as illustrated and described in conjunction
with FIG. 14) it is preferred that the sidewalls of the patterned
areas that intersect with the surface of the substrate layer 200 be
of the retrograde variety.
[0074] The substrate material is not limited to a single material
but could be an ensemble, composite, or amorphous group of one or
more materials. Thus, the particular material of the template in
which the undercut profile is formed beneath each surface feature
in the surface material can occur in any layer or combination of
layers of the substrate material. The use of multiple layers
exhibiting an undercut profile could be used as a means to provide
multiple release layers in a stack. Such an approach could thereby
extend the lifetime of the template by allowing the surface
material to be stripped revealing a "fresh" (and possibly
different) surface material. The process of forming the undercut
profile beneath each surface feature is not limited to dry etching
of the substrate material, but may also be accomplished by
exploiting the relative etch rates of the surface and substrate
materials with either isotropic or anisotropic wet etching
chemistries or by any combination of wet and dry etch chemistries.
The relative etch rates that are exploited to create the undercut
profile can be engineered as part of the template by means of using
distinct materials for the surface material and substrate material
(e.g., silicon for the substrate material and silicon nitride for
the surface material) and/or using similar materials but with
compositional differences between the surface material and
substrate material (e.g., undoped/intrinsic silicon for the
substrate material and heavily doped n-type silicon for the surface
material).
[0075] The point in the manufacturing process during which the
undercut profile beneath each surface feature is formed is not
limited to the etching of the substrate material. Rather, the
template can be comprised of a single material such as silicon
wherein a retrograde profile is formed under each surface feature
simultaneously with the formation of the surface features in the
silicon layer. This would lead to a template formed of a single
material that functions simultaneously in the roles of the
substrate material and the surface materials
Example I
[0076] A preferred thin film template 111, as generally depicted in
FIGS. 14a and 14b was created as follows in accordance with the
teachings above. Referring again to the various Figures, in this
preferred embodiment, the substrate material 200 used was silicon
having a crystalline orientation of (100), in this case, a 4-inch
silicon (100) wafer. Taking this substrate, there was then
deposited (or grown, or otherwise coated or placed) onto its
surface as a surface material 100 a 200 nm thick low-stress silicon
nitride (FIGS. 1a and 1b). A light-sensitive material, or
photoresist 300, onto the surface 4 of the surface material 100
(FIGS. 2a and 2b). In this embodiment, the photoresist 300 was spin
coated, and then heat treated using a hot plate.
[0077] Next, a photomask 400 was placed into contact with the
photoresist 300 for carrying out contact photolithographic
techniques. The photomask 400 was created to contain the desired
array of patterns which were to be transferred onto the template.
In this preferred embodiment, the photomask 400 was designed to
have an array of 2 .mu.m diameter 510 transparent circular features
500 on a 4 .mu.m pitch 530, 540 (as measured from the center 520 of
adjacent circular features 500) (FIGS. 3a and 3b). As can be seen,
the features 500 in the photomask 400 define the footprint 310 or
area of the photoresist 300 to be removed in subsequent steps. The
area of the footprint 310 exposed through each feature 500 will be
available for, e.g., selective irradiation with, e.g., UV light or
other radiation source.
[0078] Next, the masked photoresist layer of the workpiece was
subjected to UV light of an appropriate wavelength to transfer the
pattern of the photomask into the photoresist layer (FIG. 3). The
pattern in the photoresist layer 300 was developed (FIG. 4) using
standard photolithographic development techniques. As a result, the
photoresist layer became patterned so that the surface material 100
is exposed in areas 110 where it is desired to remove the surface
material. In this preferred embodiment, referring to FIGS. 6a and
6b, the transfer of the pattern from the photoresist layer 300 into
the surface material 100 in areas 110 was achieved with a Reactive
Ion Etch ("RIE") of the silicon nitride surface layer. In this
embodiment, the RIE etchant also preferably etched into the silicon
substrate layer 200 (FIG. 6).
[0079] Referring now to FIG. 9, in this preferred embodiment, the
photoresist layer 300 was stripped. The surface of the workpiece 1
was then preferably dipped in concentrated Hydrofluoric Acid to
remove any native oxide that may have formed on the exposed surface
220 of the silicon substrate layer 200. Referring still to FIG. 9,
the subsurface layer 200 was further exposed to a potassium
hydroxide (KOH) etch at 60.degree. C. for 1 minute, followed by a
deionized water (Di H2O) rinse, followed by a methanol soak and
then finally air dried. The result of such etch was the final
template structure generally depicted in FIG. 14. As shown in FIG.
14b, the KOH etched the substrate material preferentially to its
crystalline lattice thereby resulting in creation of a zone of
undercut 950 and angled sidewalls. The longer the etch time, the
more of the crystalline lattice of the substrate can be etched
away. As such, although FIG. 14 generally depicts some square
angularity in the area patterned into the substrate layer, if the
etching does not proceed as long, then the full extent of the
square angularity of the structure may not be revealed, but
instead, may present itself as more of a complex geodesic shape,
yet still having the desired undercut 950 functionality.
[0080] In yet another preferred embodiment of the present
invention, a separate substrate layer and a separate surface layer
are respectively separately patterned with, e.g., lithographic
techniques and desired patterns, followed by the steps of
overlaying the patterned surface layer onto the patterned
subsurface layer such that a preferred undercut profile is created
at the inferface between the two layers.
[0081] By using the teachings contained herein, one can make novel
reusable thin film templates. These thin film templates so made
have a number of uses (and reuses) to make thin films of any type
for any purpose. The template structure 111 provides a general
purpose method to create thin-film replicas (in any material
compatible with vacuum deposition techniques) of any pattern formed
in the template. Among the many possible applications, the template
structure disclosed herein can be used to make specimen support
films for examination of specimens with electron microscopy (e.g.
scanning electron microscope, transmission electron microscope,
scanning tunneling electron microscope, etc.) and/or scanning probe
microscopy (e.g., atomic force microscope). For example, the novel
thin film templates 111 of the present invention are ideally suited
for use as a template for the deposition and release of thin films.
That is, the undercut profile 950 causes a discontinuity to exist
in any thin film that is deposited upon the template structure 111.
The discontinuity in the deposited film resulting from the undercut
profile 950 in turn provides a mechanism for a solution to have
access to dissolve a release layer that is deposited between the
surface material 100 of the template 111 and a subsequently
deposited thin film layer. The undercut profile 950 is therefore a
key feature that allows the surface features to be replicated in
the thin film.
[0082] For example, a sacrificial release layer is typically first
deposited followed by a thin film, which both can be deposited onto
the template 111 with standard vacuum evaporation equipment. The
entire structure (template, release layer, and thin film layer) can
then be immersed into a chemical that will preferentially remove
the release layer without attacking or degrading the thin film or
the template structure 111. Once the release layer is removed, the
thin film layer will be separated from the template 111 and will
float in the solution used to remove the release layer.
[0083] In one preferred embodiment of the present invention, the
template can be used to create a thin film replica of the surface
feature(s) by means of a release layer and a replica layer where
the release layer is comprised of one or more materials deposited
upon the template by vacuum deposition techniques, the replica
layer is comprised of one or more materials deposited on top of the
release layer by vacuum deposition techniques, the materials to
form the release layer and the replica layer are any combination of
materials that can be deposited by vacuum deposition techniques
(e.g. carbon, gold, silver, beryllium, copper, nickel, aluminum,
tungsten, etc.), the release layer and replica layer materials
being chosen such that the process used to consume the release
layer does not attack the replica layer. A purpose of a thin film
replica is enable a thin film deposited on a surface and released
from the surface to obtain topography similar to the surface. Thin
films are often used as specimen supports, or structures, upon
which specimens are placed prior to TEM (transmission electron
microscopy) analysis. After placing the desired specimen on to the
specimen support, both are placed in the microscope and the
specimen is inspected/analyzed. Specimen supports are requited
since TEM specimens are often small and/or thin, and are therefore
not self-supporting. Thin carbon films are a layer of carbon with
nm-scale thickness often used as a specimen support during TEM
analysis. Thin carbon, with or without holes, is a preferred
specimen support.
[0084] Moreover, the template 111 can be reused for creating
additional thin film replicas. Without the undercut zone 950 on
each template of the present invention, an applied thin film could
not be removed as there would be no feasible manner in which to
apply a release chemical to the underlying release layer since the
thin film encapsulates the release layer. With the undercut zone
950 of the present invention, when the release layer is applied to
the surface layer 100 of the template 111 the release layer does
not form a solid layer across the surface of the template 111 this
being because the "holes" or features 500 in the template have an
undercut zone 950 around their perimeter thereby creating a
discontinuity in the release layer being applied.
[0085] As such, there are no "collars" formed from the surface down
along the edges of the patterned features in the substrate layer.
Similarly when the thin film layer is applied on top of the release
layer, these same discontinuities (undercuts 950) prevent the thin
film from forming a solid, encapsulating layer across the top
surface 100 of the template 111 and down into each feature thereby
sealing off the release layer. As such, rather than having to
sacrifice all or part of the template structure itself to achieve
release of the thin film from the template (as is done in the prior
art), the present invention permits one to subject the thin film
layer on the template to a chemical treatment (or water soluble
treatment) that will preferentially attack only the release layer,
and since this chemical treatment is able to contact the release
layer, the thin film can be released from the template 111 without
sacrificing the template structure. After the template has been
used for creation of a thin film, it can be readied for reuse.
[0086] Further, the present invention is directed to the thin films
that can be made from these novel thin film templates. As mentioned
herein, the thin films produced by the novel template described
herein could be employed in any number of applications requiring a
thin film. For example, the thin film itself could be the desired
specimen of study for use in electron microscopy, for calibration
in EM, as a filtration media, as a surface to grow materials, as a
diffraction grating, and as an antireflective coating, to name a
few. Additionally, this invention is also directed to the thin
films so created and mounted on an EM grid (e.g., copper mesh) for
use as a specimen support grid for use in electron microscopy
applications, e.g., cryo-TEM.
[0087] It should be noted that support grids comprised of a thin
carbon film with a regular array of holes supported by a copper
grid are commercially available for cryo-TEM. These carbon coated
grids are supplied almost exclusively by Quantifoil Microtools,
GmbH and are marketed under the name "Quantifoil". The template
process of the present invention is novel over and superior to
films fabricated using the prior art (see U.S. Pat. No. 6,645,744,
U.S. Pat. No. 6,821,692, and Ermantraut et al., "Perforated support
foils with pre-defined hole size, shape and arrangement,"
Ultramicroscopy 74 (1998), pp 75-81) in a number of ways.
[0088] Referring now to FIG. 15, there is outlined a preferred
process of use of the thin film template 111 described herein, and
a method of creating thin films on such template. As a first step,
one creates or otherwise obtains a thin film template according to
the teachings of the present invention 876. Certain steps may be
desired, such as cleaning the template 876 prior to use. Once the
template is readied for use, the top surface of the template is
coated with one or more release layers 880. The surface of the
template (now coated with the release layer(s) is then coated with
one or more thin film layers 882. The template, so coated, is then
subjected to the presence of a release agent to allow the thin film
to be released from the template 884. The thin film so produced is
now ready for use or other desired processing 886.
[0089] Referring now to FIG. 13c, once the template 111 is made, it
can be used in the construction or preparation of thin films. For
example, FIG. 13c illustrates the depositing of one or more release
layer(s) 850 upon the template surface layer 100, the release layer
having a total thickness 851. Addition of the release layer(s) 850
prepares the surface of the template 101 to receive one or more
deposited thin film material(s) 855 of total thickness 856. The
presence of the undercut profile 950 of the surface material 100 by
the substrate material 200 prevents both the release layer(s) 850
and the thin film layer(s) 855 from continuously coating the
surface of the template. Thus a discontinuity is formed in both the
release layer 850 and the thin film layer 855 in the zone of the
undercut profile 950 causing the pattern of the template to be
transferred into the release layer(s) 850 and the thin film
layer(s) 855. As the release layer(s) 850 and the thin film
layer(s) 855 are deposited, they will possibly extend beyond the
edges of the patterned features 102 of the surface material 100 and
form a collar of material 852, 857 around the edges of the
patterned features 102. The extent of the collars 852, 857 can be
minimized both by choosing a directional deposition method for
applying the release layer(s) 850 and the thin film layer(s) 855,
and by limiting the thickness of the surface material 100. As such,
the release layer remains exposed so that during the step of
releasing the thin film layer, the release layer can be sacrificed,
e.g., by introducing the template into an aqueous solution to
dissolve the release layer (where the release layer is of a water
soluble material). The water will be able to reach the release
layer (i.e., to get between the surface material surface 101 and
the thin film 855 since the thin film layer 855 did not encapsulate
the release layer 850. The use of the template structure described
herein provides a novel and advantageous structure for precisely
controlling the thickness of the thin film and thereby controlling
the extent of the collar of the thin-film layer(s) (855).
[0090] Carbon coated grids created with the process flow using the
novel thin films template of the present invention are superior to
carbon coated grids processed as described in U.S. Pat. No.
6,645,744, U.S. Pat. No. 6,821,692, and Ermantraut et al.,
"Perforated support foils with pre-defined hole size, shape and
arrangement," Ultramicroscopy 74 (1998), pp 75-81, in three
fundamental ways:
[0091] The perforated carbon film resulting from the use of the
invention herein would be flatter than films fabricated from prior
art (U.S. Pat. No. 6,645,744, U.S. Pat. No. 6,821,692, and
Ermantraut et al., "Perforated support foils with pre-defined hole
size, shape and arrangement," Ultramicroscopy 74 (1998), pp 75-81).
Specifically, the process by which the template film (200) is
deposited can result in nearly atomically smooth surfaces, which
transfers into the films manufactured using the process described
herein. In addition, the template manufacture process described
within allows for precise control of the thickness of layer (100),
which can be made far thinner than prior art allows (ref. U.S. Pat.
No. 6,645,744, U.S. Pat. No. 6,821,692, and Ermantraut et al.,
"Perforated support foils with pre-defined hole size, shape and
arrangement," Ultramicroscopy 74 (1998), pp 75-81). This thin film
and the undercut described within will minimize any "collars" (ref.
Downing, "Support Films with Uniform Hole Size," Microscopy Today,
11(5), p. 54, 2003) or non-uniformities that occur in prior art
(ref. U.S. Pat. No. 6,645,744, U.S. Pat. No. 6,821,692, and
Ermantraut et al., "Perforated support foils with pre-defined hole
size, shape and arrangement," Ultramicroscopy 74 (1998), pp 75-81)
and will allow more optimal ice for cryoTEM imaging (Downing,
"Support Films with Uniform Hole Size," Microscopy Today, 11(5), p.
54, 2003).
[0092] Because the template is not consumed during the film
manufacturing process described within, and because the films are
completely removed from the surface of the template, contamination
of the films created can be minimized. Prior processes (U.S. Pat.
No. 6,645,744, U.S. Pat. No. 6,821,692, and Ermantraut et al.,
"Perforated support foils with pre-defined hole size, shape and
arrangement," Ultramicroscopy 74 (1998), pp 75-81) can result in
carbon containing resides left on the surface of the films (ref.
Downing, "Support Films with Uniform Hole Size," Microscopy Today,
11(5), p. 54, 2003.) The template process described within will
minimize or eliminate these forms of contamination, resulting in
more optimal ice formation for cryoTEM imaging (see Harris,
"Carbonaceous Contaminants on Support Films for Transmission
Electron Microscopy," Carbon, 39(6), pp 909-913, 2001 and Downing,
"Support Films with Uniform Hole Size," Microscopy Today, 11(5), p.
54, 2003).
[0093] The carbon coated grids that can be created from the use of
the invention described herein are clean by construction since the
template itself can be aggressively cleaned (e.g. with acids,
solvents, and/or oxygen plasma) and the surface of the thin carbon
film upon which a sample will be in contact is not exposed to
contaminates during the grid formation process. The cleanliness of
carbon coated grids for EM created from the use of the invention
described herein are superior to EM grids available in prior art
due to the known contamination problems of prior art EM grids (see
Harris, "Carbonaceous Contaminants on Support Films for
Transmission Electron Microscopy," Carbon, 39(6), pp 909-913, 2001
and Downing, "Support Films with Uniform Hole Size," Microscopy
Today, 11(5), p. 54, 2003).
[0094] The following represents an exemplary list of
references.
TABLE-US-00001 U.S. Patent References [1] 2,347,965 May 1944
Ramberg 250/49.5 [2] 2,572,497 October 1951 Law 18/57 [3] 2,875,341
February 1959 Nesh 250/49.5 [4] 4,250,127 February 1981 Warren, et
al. 264/22 [5] 5,004,920 April 1991 Lee, et al. 250/304 [6]
6,645,744 November 2003 Ermantraut, et al. 435/183 [7] 6,821,692
November 2004 Ermantraut, et al. 430/17 Other References [8]
Ermantraut, E; Wolfhart, K; and Tichelaar, W, "Perforated support
foils with pre-defined hole size, shape and arrangement,"
Ultramicroscopy 74 (1998), pp 75-81. [9] Downing, K, "Support Films
with Uniform Hole Size," Microscopy Today, 11(5), p. 54, 2003. [10]
Harris, P, "Carbonaceous Contaminants on Support Films for
Transmission Electron Microscopy," Carbon, 39(6), pp 909-913,
2001
[0095] As can be learned from the disclosures herein, a novel
method of making thin film templates has been disclosed. The
templates created by the process described herein are reusable.
Additionally, there is described herein a novel template structure
that is re-useable for creation of thin films. The use of the
template for making thin films, as well as the thin films
themselves are objects of the present invention. Furthermore, end
use applications for using thin films created using the present
invention are also the subject of the present invention.
[0096] All references referred to herein are incorporated herein by
reference. While the apparatus and methods of this invention have
been described in terms of preferred embodiments, it will be
apparent to those of skill in the art that variations may be
applied to the process and system described herein without
departing from the concept and scope of the invention. All such
similar substitutes and modifications apparent to those skilled in
the art are deemed to be within the scope and concept of the
invention. Those skilled in the art will recognize that the method
and apparatus of the present invention has many applications, and
that the present invention is not limited to the representative
examples disclosed herein. Moreover, the scope of the present
invention covers conventionally known variations and modifications
to the system components described herein, as would be known by
those skilled in the art. While the apparatus and methods of this
invention have been described in terms of preferred or illustrative
embodiments, it will be apparent to those of skill in the art that
variations may be applied to the process described herein without
departing from the concept and scope of the invention. All such
similar substitutes and modifications apparent to those skilled in
the art are deemed to be within the scope and concept of the
invention as it is set out in the following claims.
* * * * *