U.S. patent application number 11/638137 was filed with the patent office on 2007-07-26 for method of electrolytically depositing materials in a pattern directed by surfactant distribution.
Invention is credited to Noshir Sheriar Pesika, Peter Searson, Kathleen Joan Stebe.
Application Number | 20070170064 11/638137 |
Document ID | / |
Family ID | 34381930 |
Filed Date | 2007-07-26 |
United States Patent
Application |
20070170064 |
Kind Code |
A1 |
Pesika; Noshir Sheriar ; et
al. |
July 26, 2007 |
Method of electrolytically depositing materials in a pattern
directed by surfactant distribution
Abstract
In accordance with the invention, a surface of a substrate is
patterned by the steps of providing the substrate, forming a
surfactant pattern on the surface and using electroless deposition
or electrodeposition to deposit material on the surface in a
pattern directed by the surfactant pattern. The material will
preferentially deposit either under the surfactant pattern or
outside the surfactant pattern depending on the material and the
conditions of deposition. The surfactant pattern is conveniently
formed by printing on the surface a surfactant that forms a self
assembled monolayer (SAM). The method can be adapted to build
complex structures in one, two and three dimensions.
Inventors: |
Pesika; Noshir Sheriar;
(Baltimore, MD) ; Stebe; Kathleen Joan;
(Baltimore, MD) ; Searson; Peter; (Baltimore,
MD) |
Correspondence
Address: |
PATENT DOCKET ADMINISTRATOR;LOWENSTEIN SANDLER PC
65 LIVINGSTON AVENUE
ROSELAND
NJ
07068
US
|
Family ID: |
34381930 |
Appl. No.: |
11/638137 |
Filed: |
December 13, 2006 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10836021 |
Apr 29, 2004 |
|
|
|
11638137 |
Dec 13, 2006 |
|
|
|
60467248 |
May 1, 2003 |
|
|
|
60523498 |
Nov 19, 2003 |
|
|
|
Current U.S.
Class: |
205/118 |
Current CPC
Class: |
C23C 18/1603 20130101;
C23C 18/1608 20130101; B82Y 30/00 20130101; C23C 18/1651 20130101;
H05K 3/185 20130101; C25D 5/10 20130101; B82Y 40/00 20130101; H05K
3/182 20130101; C23C 18/34 20130101; C23C 18/1605 20130101; C25D
5/02 20130101; C25D 5/022 20130101; C23C 18/44 20130101 |
Class at
Publication: |
205/118 |
International
Class: |
C25D 5/02 20060101
C25D005/02 |
Goverment Interests
GOVERNMENT INTEREST
[0002] This invention was made with government support under NASA
Contract NGT5-50372. The government has certain rights in the
invention.
Claims
1. A method of electrolytically depositing materials on a substrate
surface in a pattern comprising the steps of: providing the
substrate; forming a surfactant pattern on the surface; depositing
material on the surface by electrodeposition, the material
deposited in a pattern corresponding to the surfactant pattern or
its complement.
2. The method of claim 1 wherein the substrate comprises a
conductive, semiconductive, or insulating material.
3. The method of claim 1 wherein the substrate surface is
substantially planar.
4. The method of claim 1 wherein the substrate surface is
curved.
5. The method of claim 1 wherein forming the surfactant pattern
comprises forming a self-assembled monolayer of surfactant.
6. The method of claim 1 wherein forming the surfactant pattern
comprises contacting the surface with a surfactant-bearing stamp
configured to print the pattern on the surface.
7. The method of claim 1 wherein forming the surfactant pattern
comprises covering at least a portion of the surface with a
continuous coating of surfactant and removing one or more portions
of the continuous coating to form the pattern.
8. The method of claim 7 wherein the removing is by UV light
exposure.
9. The method of claim 7 wherein the removing is by a scanning
probe.
10. The method of claim 1 wherein the material is deposited on the
surface in a pattern corresponding to the surfactant pattern.
11. The method of claim 6 wherein forming the surfactant pattern
comprises contacting the surface a plurality of times with at least
one surfactant bearing stamp.
12. The method of claim 1 further comprising at least one
additional deposition in accordance with claim 1.
13. The method of claim 12 wherein one deposition is in the pattern
of the surfactant and the other deposition is in the form of the
complement of the surfactant pattern.
14. The method of claim 12 wherein the material of the additional
deposition is different from the material of the first
deposition.
15. The method of claim 1 wherein the depositing of material
comprises selecting a deposition potential to determine whether the
material is deposited in a pattern corresponding to the surfactant
pattern or in a pattern corresponding to the complement of the
surfactant pattern.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a divisional of U.S. patent application Ser. No.
10/836,021 filed on Apr. 29, 2004 entitled "Method of
Electrolytically Depositing Materials in a Pattern Directed by
Surfactant Distribution", which is hereby incorporated herein by
reference. U.S. patent application Ser. No. 10/836,021, in turn,
claims the benefit of U.S. Provisional Application Ser. No.
60/467,248 filed on May 1, 2003 by the present inventors and
entitled "Patterned Deposition of Materials as Directed by
Surfactant Distribution on Electrodes". It also claims the benefit
of identically titled Provisional Application Ser. No. 60/523,498
filed by the present inventors on Nov. 18, 2003. Both provisional
applications are incorporated herein by reference.
FIELD OF THE INVENTION
[0003] This invention relates to lithography and, in particular, to
a method of high resolution lithography using a surfactant pattern
to direct the electrolytic deposition of materials on a substrate
surface. The process can be used to produce structures patterned in
one, two and three dimensions.
BACKGROUND OF THE INVENTION
[0004] Lithographic processes are crucial for the manufacture of
many microelectronic, optical and nanoscale devices, including
computer chips, data storage devices, flat screen displays and
sensors. Lithographic processes are used to create patterned areas
on the surface of a substrate which, in turn, can be further
processed as by etching, doping, oxidizing, growing or other
processing to form the features of a desired component, circuit or
other device.
[0005] The competitive pressure to increase the functionality of
such devices has required smaller and smaller patterns. As a
consequence, manufacturers are pressing the limits of conventional
optical and electron beam lithography. Optical lithography forms a
pattern by exposing a photoresist to light through an exposure
mask. As is well known, optical lithography is limited by the
wavelength of the exposure light. Shorter wavelength light, now in
the ultraviolet range, is being used to expose smaller patterns,
but the shorter the wavelength, the more complex and expensive the
equipment required to generate the light and pattern the
substrate.
[0006] Electron beam lithography (e-beam lithography) forms a
pattern on a resist-covered substrate by projecting an electron
beam line-by-line onto the resist to form the pattern. However
e-beam lithography is limited in resolution by the need for special
stencil masks and, because of its line-by-line exposure, is too
limited in speed for satisfactory manufacturing. Moreover both
optical and electron beam lithography typically use polymer resists
which require time consuming steps to develop and remove.
[0007] Accordingly there is a need for simpler, faster and less
expensive processes for high resolution lithography.
SUMMARY OF THE INVENTION
[0008] In accordance with the invention, a surface of a substrate
is patterned by the steps of providing the substrate, forming a
surfactant pattern on the surface and using electroless deposition
or electrodeposition to deposit material on the surface in a
pattern directed by the surfactant pattern. The material will
preferentially deposit either under the surfactant pattern in the
pattern of the surfactant or outside the surfactant pattern in the
complement of the surfactant pattern depending on the material and
the conditions of deposition. The surfactant pattern is
conveniently formed by printing on the surface a surfactant that
forms a self assembled monolayer (SAM). The method can be adapted
to build complex structures in one, two and three dimensions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The nature, advantages and various additional features of
the invention will appear more fully upon consideration of the
illustrative embodiments of the invention described in detail in
connection with the accompanying drawings. In the drawings:
[0010] FIG. 1 is a schematic block diagram showing the steps in
patterning a surface of a substrate in accordance with the
invention;
[0011] FIGS. 2A, 2B and 2C illustrate steps of an advantageous
method of forming a pattern of surfactant on a substrate;
[0012] FIGS. 3A, 3B show apparatus for electrodeposition and for
electroless deposition respectively;
[0013] FIG. 4 schematically illustrates a stamp for forming a
surfactant pattern on a substrate;
[0014] FIG. 5 is an AFM image of a pattern of electrodeposited
material;
[0015] FIG. 6 is an AFM image of a pattern of electrodeposited
material;
[0016] FIGS. 7A, 7B and 7C are a series of AFM images of material
deposited at various deposition potentials.
[0017] FIG. 8 is an AFM image of nanoscale-width deposited
stripes;
[0018] FIG. 9 illustrates adaptation of the FIG. 1 process to grow
a second material between stripes of a first material;
[0019] FIGS. 10A and 10B show a multicomponent structure formed by
the process of FIG. 1;
[0020] FIG. 11 illustrates adaptation of the FIG. 1 process to form
a composite 3D structure;
[0021] FIGS. 12A and 12B are AFM images of a composite 3D structure
made by the FIG. 1 process; and
[0022] FIG. 13 is an AFM image of a grid pattern of silver produced
by electroless deposition on a silver substrate patterned with an
octanethiol SAM.
[0023] It is to be understood that the drawings are for
illustrating the concepts of the invention and, except for the
micrographs, are not to scale.
DETAILED DESCRIPTION
[0024] A. The Basic Process
[0025] Referring to the drawings, FIG. 1 is a block diagram showing
the steps involved in forming a pattern of material on the surface
of a substrate. The first step, shown in block A, is to provide a
substrate having the surface to be patterned. For
electrodeposition, the substrate advantageously comprises a
conductive or semiconductor material such as a surface layer of
metal. The surface can be an insulator or metal if electroless
deposition is used.
[0026] The next step, Block B, is to form a surfactant pattern on
the surface of the substrate. The pattern is advantageously formed
by printing with a stamp a thin surfactant layer that forms a
self-assembled monolayer or SAM on the surface. The stamp (referred
to as a PDMS stamp) preferably has microscale or nanoscale pattern
features. Exemplary surfactants include thiols for gold and silver
and isocyanides for platinum and palladium. The stamp can be
conveniently fabricated using techniques well known in the art. An
alternative approach to forming the surfactant pattern is to apply
a continuous film of surfactant on the surface and to remove
selected portions as by masked UV exposure or with an atomic force
microscope tip.
[0027] FIGS. 2A through 2C depict steps of an advantageous method
of forming the pattern of surfactant on the substrate. As shown in
FIG. 2A, a patterned stamp 20 is provided and coated with
sufficient surfactant solution 21 to cover that patterned surface.
The surfactant is dried to a thin coating 22. The next step (FIG.
2B) is to bring the stamp with surfactant coating 22 into contact
with the surface 23 of the substrate 24. As shown in FIG. 2C, the
stamp is then lifted off the surface 23 leaving surfactant pattern
25 on the surface. The substrate surface is preferably planar, but
can be curved if flexible stamping is used.
[0028] Referring back to FIG. 1, the third step shown in Block C is
to electrodeposit material in a pattern directed by the surfactant
pattern. The material can be preferentially deposited underlying
the surfactant in the form of the surfactant pattern or it can be
preferentially deposited outside the surfactant pattern, leaving
the pattern substantially free of the material. Which of these
processes occurs, corresponding to negative and positive resist
processes, depends on the deposition conditions.
[0029] We have demonstrated that silver can be deposited onto a
gold or silver substrate patterned with octadecanethiol in either
positive or negative resist mode depending on the deposition
potential. Positive resist mode deposition corresponds to
deposition in the regions where there is no surfactant. Negative
resist mode deposition occurs where the deposition is in the
regions where there is surfactant. The ability to operate in both
positive and negative resist mode provides many attractive
possibilities in depositing complex structures in three dimensions
with different materials.
[0030] As an alternative to the electrodeposition of Block C, the
material can be deposited in a pattern directed by the surfactant
pattern using electroless deposition (Block D).
[0031] FIG. 3A shows apparatus 36 for electroless deposition to
produce a patterned material on a substrate 37. The substrate 37,
which can be an insulator, is patterned with surfactant (ODT). It
is disposed within an electroless deposition solution 38 within a
container 39. A typical electroless bath for depositing silver is a
solution containing 450 g/L of silver nitrate, 444 g/L of Rochelle
salt, 64 mL/L saturated ammonia solution, and 31 g/L of Epsom salt.
FIG. 13 is an AFM plan view image of a silver grid deposited onto
an ODT patterned silver substrate by electroless deposition.
[0032] FIG. 3B is a schematic illustration of apparatus 30 for
electrodeposition of a material onto the surface 23 of a substrate
24. In essence, the apparatus 30 comprises a container 31 enclosing
an electrolytic bath 32. The surface 23 with surfactant pattern 25
is disposed in physical contact with the bath 32 and in electrical
contact with a working electrode 33. The apparatus further
comprises a counter electrode 34 to provide deposition current and
a reference electrode 35 for measurement and control. A voltage
source (not shown) drives deposition current between electrodes 33
and 34 to effect deposition.
[0033] The invention may now be more clearly understood by
consideration of the following specific examples.
EXAMPLE 1
[0034] A substrate was prepared comprising a silicon wafer
supporting a 100 nm gold film coated on a sublayer of chromium. The
1 inch square substrate was cleaned by rinsing with ethanol and
blow drying with pure nitrogen gas.
[0035] A pattern of surfactant was formed on the gold surface by
the printing technique of FIG. 2. A PDMS stamp was made by the
procedure described in A. Kumar et al., "Patterning Self-Assembled
Monolayers: Applications in Materials Science", Langmuir (1994),
10, 1498-1511. FIG. 4 is a schematic illustration of the PDMS stamp
40 comprising a body 41 having a patterned surface 42 composed of
3-4 micrometer projecting regions 43 separated by 6-7 micrometer
recessed regions 44.
[0036] The PDMS stamp was oriented so that the patterned features
were on top. The patterned face of the stamp was then coated with a
1-10 mM solution of octadecanethiol (ODT) dissolved in ethanol.
After 1 min. the stamp was blow dried with nitrogen gas. The stamp
was then placed with the features face-down onto the gold surface,
and sufficient pressure was applied to provide complete contact of
the patterned stamp surface to the gold surface. After 15 sec, the
stamp was lifted off and the gold surface was rinsed with ethanol
and blow dried with nitrogen gas. This patterning left a pattern of
hydrophobic regions produced by a SAM of the ODT and surrounding
hydrophilic regions of bare gold.
[0037] Material was then electrodeposited on the gold surface in a
pattern directed by the surfactant pattern. Specifically, an
electroplating cell similar to that of FIG. 3 was set up with a
silver plating bath composed of an aqueous solution of 20 mM KAg
(CN).sub.2, 0.25 M NaCO.sub.3 buffered to pH 13 with NaOH. The gold
surface and the counter electrode were then connected to a
potentiostat system using a potential of -0.7 volts as compared
with an Ag/AgCl reference electrode to deposit silver on the
substrate surface. After deposition of the desired thickness, the
set up was disassembled and the substrate was rinsed with distilled
water. The silver deposited underneath the SAM surfactant in the
same pattern as the printed surfactant pattern. FIG. 5 is an atomic
force microscopy (AFM) image of the striped pattern of high silver
regions 50.
EXAMPLE 2
[0038] Example 2 used the same set up as Example 1 except that a
bath for depositing nickel was used. Specifically the bath was a
solution of 20 gL.sup.-1 NiCl.sub.2.6H.sub.2O, 500 g L.sup.-1
Ni(H.sub.2NSO.sub.3).sub.2.4H.sub.2O and 20 g
L.sup.-1H.sub.3BO.sub.3, buffered to pH 3.4. FIG. 6 is an AFM image
of the high nickel regions. The nickel 60 deposited on the areas
not covered by the printed surfactant.
EXAMPLE 3
[0039] The ODT SAM on a gold or silver substrate can be tuned to
act as either a positive or negative resist for the deposition of
Ag. At potentials more positive than -0.45 volts as compared with
an Ag/AgCl (3M NaCl) reference electrode, the ODT SAM is intact and
acts like a positive resist preventing the deposition of Ag the ODT
SAM is present. In this case, deposition occurs only on the bare
substrate surface. This process (positive resist mode) works for
many other metals (e.g. Cu, Ni, Pt) but the potential range and
lower limit are different for different metals.
EXAMPLE 4
[0040] By tuning the deposition potential to more potentials more
negative than -0.6 volts as compared with an Ag/AgCl (3M NaCl)
reference electrode Ag will deposit underneath the patterned
surfactant.
[0041] FIGS. 7A, 7B and 7C are a series of AFM topographic images
showing how it is possible to tune the ODT SAM from acting as a
positive resist to silver to being a negative resist. In FIG. 7A at
a deposition potential of -0.65 volts as compared with an Ag/AgCl
(3M NaCl) reference electrode the ODT SAM behaves as negative
resist. In FIG. 7C at -0.45 volts as compared with an Ag/AgCl (3M
NaCl) reference electrode the ODT SAM behaves as a positive
resist.
EXAMPLE 5
[0042] Similar tuning by deposition potential has been demonstrated
for the deposition of Ag on a gold patterned gold electrode.
EXAMPLE 6
[0043] By optimizing the deposition and distribution of the
surfactant on the surface of the substrate and the deposition
conditions, features of about 400 nm wide (silver stripes) were
deposited on a SAM patterned gold surface. FIG. 8 is an AFM image
showing the topography of the stripes.
[0044] B. Fabrication of Two Dimensional Patterns
[0045] While one exemplary application of the FIG. 1 process is in
the fabrication of a simple linear array grating, more complex two
dimensionally varying patterns can be fabricated. For example,
complex stamp patterns with two-dimensionally varying patterns can
be fabricated by e-beam lithography and used to print patterns of
surfactant prior to electrodeposition or electroless deposition of
positive or negative patterns.
[0046] Another approach that can be used with even very simple
stamp patterns is to apply plural successive stampings with rotated
or different stamp patterns. For example, if the stamp of FIG. 4 is
axially rotated by 90.degree. and applied a second time before
growth, then a two dimensional grid of lines can be grown.
[0047] Yet another approach is to take advantage of the fact that a
surfactant may act as a positive resist for one material and a
negative resist for another. FIG. 9 illustrates a variation of the
process wherein a substrate having a SAM pattern serves like a
negative resist for the electrolytic growth of a silver pattern 91
and a positive resist for the electrolytic growth of nickel 92,
filling the spaces between the silver lines.
EXAMPLE 7
[0048] The capability of tuning the resist from being a positive
resist to being a negative resist has been exploited to create
multi-component structures. A multicomponent structure comprising
alternating Ag and Cu stripes was created by first using the ODT
SAM pattern as a positive resist for the deposition copper followed
by the deposition of silver in the negative resist mode. FIGS. 10A
and 10B depict the resulting structure 100 in two different levels
of magnification, showing the Cu stripes 101 and Ag stripes
102.
[0049] C. Fabrication of Three Dimensional Structures
[0050] Even more complex three-dimensional structures can be
fabricated by applying the process of FIG. 1 multiple times to
produce a composite 3D structure. FIG. 11 illustrates a process for
making a three-dimensionally varying structure by multiple
applications of the FIG. 1 process. The first FIG. 1 process grows
a first pattern 110 on the substrate. The surfactant 111 is removed
as by exposure to UV light or by the application of a large
negative potential (e.g. -1V) to the substrate. Then a second SAMs
pattern is printed on the grown pattern 110 to control a second
growth step of a pattern corresponding to the intersection of the
second SAMs pattern 112 and the high regions of the first pattern
110. This is essentially two successive FIG. 1 processes.
EXAMPLE 8
[0051] Silver was deposited on a silver substrate in a two step
process. In the first step, silver was deposited using a SAM
pattern in the positive resist mode to create rows of Ag. In the
second step, the same sample was stamped at 90 degrees rotation to
create a segmented layer of ODT on the first layer of Ag stripes
but perpendicular thereto. The deposition step resulted in pillars
of Ag deposited only on the base Ag surface of the first layer of
silver stripes. FIG. 12A is an AFM image of the resulting
structure. FIG. 12B is a schematic drawing showing the stripes and
pillars of the structure.
[0052] It can now be seen that we have developed a technique that
involves the patterning of a surface with a surfactant and then
using electrodeposition or electroless deposition, depositing a
pattern of material that is directed by the surfactant. For
electrodeposition, at certain potentials, the deposition occurs in
the regions where no surfactant is adsorbed (we call this positive
resist mode by analogy to photolithography). At other potentials,
deposition occurs underneath the surfactant (we call this a
negative resist mode).
[0053] There are three important components: the substrate, the
surfactant, and the depositing material. The surfactant couples to
the surface, as by forming a monolayer on the surface (e.g. a
self-assembled monolayer). In positive resist mode using
electrodeposition, a wide range of materials can be deposited,
including elemental metals, alloys, electronically conducting
polymers, and some metal oxides and semiconductors including
magnetic materials which are of interest in magnetic recording.
Electroless deposition can be performed in positive resist mode.
The potential advantage here is that it can be done on an
insulator. We have demonstrated electroless deposition on a silver
substrate. The ability to pattern an insulating surface and to
deposit patterned structures thereon can be technologically
important.
[0054] This process is not limited to deposition on a flat
substrate. Since micro-contact printing (stamping) uses a flexible
stamp, it can be applied to curved surfaces.
[0055] It is 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.
* * * * *