Download Atomic Force Microscope (AFM)

NANOFABRICATION USING
ATOMIC FORCE MICROSCOPY
Ampere A. Tseng
Professor of Engineering
Arizona State University, Tempe, Arizona 85287 USA
E-mail: [email protected]
Co-Workers: L.A. Abril-Herrera, A.O. Adebo, C. Chaidilokpattanakul , R. V. Edupuganti ,
Ravi Gupta, Ivan A. Insua, C. J. Johnson, J. D. Kaplan, M. H. Lee, Bharath Leeladharan,
Bo Li, W. D. Nath, Jong S. Park, Masahito Tanaka, C. L. Thomas, George P. Vakanas
Collaborators: Professor Tu Pei Chen, Nanyang Technological University, Singapore
Professor Rudy Diaz, Arizona State University, USA
Dr. Shyankay Jou, National Taiwan University of Science and Technology, ROChina
Dr. Gary Li, Freescale Semiconductor, USA
Dr. Zhuang Li, Chinese Academy of Sciences, PRChina
Professor M. F. Luo, National Central University, ROChina
Dr. Andrea Notargiacomo, Roma TRE University, Italy
Professor Jun-ichi Shirakashi, Tokyo University of Agriculture & Tech, Japan
Sponsors: US National Science Foundation,
Freescale Semiconductor, Intel, Pacific Technology, Walsin Lihwa
WHAT IS AFM-BASED NANOFABRICATION
♦ AFM-based nanofabrication is using a
functionalized cantilevered-tip for performing
nanofabrication.
♦ Nanofabrication aims at building nanoscale
structures (0.1 – 100 nm), which can act as
components devices,
components,
devices or systems with desired
properties, performance, reliability,
reproducibility, in large quantities at low cost.
• Methodology or Processing Technology
• Toolbox (Equipment: hardware, software, system)
• Nanostructured Materials or Raw Materials
• Physical Product (Components, device,
system….)
Ampere A. Tseng, 2010
Atomic Force Microscope (AFM)
AFM-Based Nanofabrication: Milestones
ƒ 1982: Scanning Tunneling Microcopy (STM) invented by Binnig,
Rohrer, and Gerber (1986 Nobel Physics Prize).
ƒ 1986: Atomic Force Microcopy invented by Binnig (US Patent
4,724,318).
ƒ 1990s: Lithography Using Scanning Tunnelling Micoscopy (STM)
and AFM.
ƒ 2000s: Lithography Using Scanning Near-Field Optical Microscopy
(SNOM) and Dip Pen Nanofabrication (DPN).
ƒ 2008: APMC (led by Zyvex Labs) Awarded US$9.7 Millions by DARPA
& Texas ETF for Commercialization of Tip Based Nanofabrication
(TBN) (focusing on AFM).
ƒ 2009/10 DOE Solicitation Upcoming.
•
AFM works on insulating materials at room environment and is the most widely used
scanning probe microscope (Low cost!!)
•
The AFM combines the technology developed for the surface profiler with the scanning
tunnelling microscope.
Ampere A. Tseng, 2010
ƒ 2009/10 NSF Solicitation Upcoming.
ƒ 2009-2013: $100 million in 5 years in USA.
Ampere A. Tseng, 2010
NANOFABRICATION AND TECHNOLOGY
Length scale realizable in nanofabrication
Intel® 300mm wafer)
Intel® 22 nm
test chip
(SRAM
arrays and
logic
peripheral
circuits) with
364 Mb array
size and 2.9
billion
transistors
Ampere A. Tseng, 2010
Ampere A. Tseng, 2010
1
World Nanoproduct Market
Ampere A. Tseng, 2010
http://nanopedia.case.edu/image/nanoscale.jpg
Semiconductor Related Markets
• Semiconductor world market grew by 6 % to
$249 billion in 2006 and is $267 billion in
2007 and is expected to rise to 274 billions
by 2008 (by Semiconductor Industry Association and IT research firm)
• MEMS (MicroElectroMechanical Systems)
companies: 80 in 1997 and 8,000 in 2007 in
USA
• World market of MEMS is $48 billion in 2005,
and is expected to rise to $72 billion by 2008
and $95 billion by 2010 (In.Stat, An Industry in Transition:
2007 MEMS Forecast, Scottsdale, AZ)
• Market Size of Nanoelectronics is US$ 1.8 Billion in 2005
and is forecasted to reach US$ 4.2 Billion by the year 2010.
• Nanofood market will have an annual growth rate of 30.94%
from 2006 to 2010 with a market value of US$ 20.40 Billion
by 2010.
• The market for textiles using nanotechnology will cross
US$ 13.6 billion mark by 2007. By 2012, the market is
expected to reach US$ 115 Billion.
• US market for nanotech tools is projected to increase by
nearly 30% per year with US$ 0.9 Billion in 2008, and to US$
2.7 Billion in 2013.
• US has the largest share of global investment in
Nanotechnology. The US market had a share of 28% in
2005, followed by Japanese market with about 24% share.
The western European market also had a quarter of the
market share with major investment in countries like
Germany, UK and France. Other countries like China, South
Korea, Canada and Australia held the rest of the share.
(The World Nanotechnology Market, Global Information Inc, 2006)
General Nanotechnology
Related Markets
US National Science Foundation has made
predictions of the of nanotechnology by 2015
• $340
$
billion for nanostructured
materials,
• $600 billion for electronics and
information-related equipment,
• $180 billion in annual sales from
nanopharmaceuticals
Ampere A. Tseng, 2010
Techniques in AFM-based Nanofabrication
ƒ Atomic Force Microscopy (AFM)
TYPICAL ATOMIC FORCE MICROSCOPE
Digital Instruments Nanoscope IIIA
* Nano-Manipulation: Atoms, molecules, Nanoparticles,
nanoclusters…
* Material Removal: Mechanical scratch, etching..
* Material Modification: Resist exposure, anodic oxidation,..
* Material Deposition and Growth: Electrical field-induced masstransfer, electrochemical deposition.
♦Dip-Pen Nanolithography (DPN)
♦Scanning Near-field Optical Microscopy
(SNOM)
1. Tseng, A. A., Notargiacomo, A., and Chen, T. P. (2005), “Nanofabrication by scanning probe microscope lithography: a review,”
J. Vac. Sci. Technol. B, Vol. 23, No. 3, pp. 877-894.
2. Tseng, A. A. (2007), “Recent developments in nanofabrication using scanning near-field optical microscope lithography,”
Optical & Laser Tech, Vol. 39, No. 3, pp. 514-526.
3. Tseng, A. A. and Li, Z. (2007), “Manipulations of atoms and molecules by scanning probe microscopy,” J. Nanoscience &
Nanotechnology, Vol. 7, No. 8, pp. 2582-2595 .
Ampere A. Tseng, 2010
2.5 x 2.5 nm simultaneous topographic
and friction image of highly oriented
pyrolytic graphic (HOPG). The bumps
represent the topographic atomic
corrugation, while the coloring reflects
the lateral forces on the tip. The scan
direction was right to left
Ampere A. Tseng, 2010
2
FUNCTIONALITY OF AFM TIP
Interaction Between Atoms or Molecules
STM: d = tip gap
Atoms & Molecules
Feedback signal
is the current (I)
After discovered by Lord van der Waals, the
vdW force was quantified by London (1930). The
potential of the vdW interaction (pv) can be
approximated as
pv ( z ) = − A1 / z 6
AFM: d = tip gap
Feedback signal
is the force (F)
London forces (ven der Waals) arise from the temporary
variations in electron density around atoms and non-polar
molecules (1) depicts the average electron clouds of two nonpolar
molecules. However at any instant the electron distribution
around an atom or molecule will likely produce a dipole moment
(2) which will average out to zero over a period of time. But even
a temporary or transient dipole moment can induce a (temporary)
dipole moment in any nearby molecules (3) causing them to be
attracted to the first molecule.
Presently AFM is loaded with forces and
electric voltages in ambient environment
Ampere A. Tseng, 2010
Three Modes of Operation
• Contact mode: also known as static
mode, an AFM tip makes soft
"physical contact" with the sample.
The tip is attached to the end of a
cantilever with a low spring constant.
The contact force causes the
cantilever to bend to accommodate
changes in topography.
Measurement: displacement (δ)
Feedback signal: force (F) = kδ
• Intermittent contact mode: also
known as tapping mode, the
cantilever is driven to oscillate up and
down at near its resonance frequency
by a small piezoelectric element
mounted in the AFM tip holder. The
amplitude of this oscillation is greater
than 10 nm, typically 100 to 200 nm. A
tapping AFM image is therefore
produced by detecting the force of
the oscillating contacts of the tip with
the sample surface.
Ampere A. Tseng, 2010
AFM HEIGHT
IMAGES
Topographical 3D
Rendering of Red
Blood Cells. Raw
atomic force
microscope data is
visualized as 3D
surface
Data by Janelle Gunther, 3D Rendering by Ben Grosser
(in www.itg.uiuc.edu/exhibits/gallery)
Ampere A. Tseng, 2010
(1)
where A1 is the interaction constant defined by
London (1930) and dependent on the
polarization and ionization potential
associated and z is the distance between the
centers of the paired atoms. In general, the
above equation is effective only up to several
tens nm. When the interactions are too far
apart the dispersion potential, pv, decays
faster than 1/z6; this is called the retarded
regime (Israelachvilli, 1991).
Ampere A. Tseng, 2010
Operation Modes and Van der Waals Curve
AFM can be operated in three different
modes. Each mode is operated in a
different level of Van der Waals force
Operated at Frequency Modulation
or Amplitude Modulation
Measurement:
displacement, δ = δ(t)
Feedback signal:
dynamic force, Fd = F(k, δ, t)
• Non-contact (NC) mode: also known as
dynamic mode, the cantilever is vibrated
near but not contact to the sample surface
at a frequency slightly above its resonance
frequency (typically, 100 - 400 kHz) ) where
its amplitude is typically a few nm. Due to
interaction of forces acting on the
cantilever when the tip comes close or
taps to the surface (within 10 nm), Van der
Waals force or other forces (~1012 N) act to
decrease the resonance frequency of the
cantilever. This decrease in resonance
frequency combined with the feedback
loop system maintains a constant
oscillation amplitude or frequency by
adjusting the average tip-to-sample
distance. Measuring the tip-to-sample
distance at each data point allows the
scanning software to construct a
topographic image of the sample surface.
The absence of repulsive forces in NC
mode permits its use in the imaging “soft”
samples.
Ampere A. Tseng, 2010
IMAGING COMPARISON OF AFM AND SEM
(AFM)
(SEM)
Atomic Force Microscopy
- Contrast on flat samples
- 3D magnification
- Works in ambient air
Scanning Electron Microscopy
- Good depth of field
- Fast scanning
- 2⅓D magnification
Ampere A. Tseng, 2010
3
Electric & Magnetic Forces Map by AFM
Electrostatic Potential and Forces
● The Lennard-Jones potential is important for the
interaction between neutral atoms or molecules.
The electrostatic interaction force becomes
important, if the particles are electrically charged
and conductive.
The corresponding
Coulomb force (Fe)
between two charges
can be found as:
−q
Fe =
● Frequently, in calculating the interaction forces,
the molecules with permanent dipoles can be
treated as point charges.
15μm scan Electric Force images showing reversed tip bias from A to B
of polarized ferroelectric domains in an epitaxial, single crystalline
Pb(Zr0.2Ti0.8)O3 thin film. The polarization pattern was created using the
same metal-coated AFM tip that moments later captured these images
(corresponding topography is featureless (not shown), with 0.2nm RMS
roughness). Courtesy of T. Tybell, C.H. Ahn, and J.M. Triscone,
1 q2
4πε 0 r 2
The total interaction force can be found by integrating
all charged particles involved. Analytical integration
solutions do existing for very limited simple cases.
The formula developed by Law and Rieutord (2002)
● An appropriate understanding of electrostatic
for a conical tip with a spherical apex of r0 and a
forces is of a wide interest for better controlling the
electromagnetic induced reactions and the related rectangular include angle, 2θ is selected:
Fe = πε 0V z ( zd )
charging mechanisms in performing many AFMbased nanopatterning processes, such as local
where V is the applied voltage and z(zd) is a
anodic oxidation and electrostatic nanolithography geometrical function including the contributions from
as well as Kelvin probe microscopy.
the spherical apex and conical part of the tip and the
cantilever (as shown in the attached figure). By
● The electrostatic potential (pe), also known as
assuming θ = 0, an approximation for z(zd) adopted by
Coulomb potential, is an effective pair potential
Butt et al. (2005) can be applied here. Then, the
that describes the interaction between two point
electrostatic force becomes:
charges. It acts along the line connecting the two
r02V 2
charges (q1, q2):
q1q2
F = πε
pe =
4πε 0 r
where r is the distance between two charges and ε0
is the electric constant (permittivity of free space).
B.M. Law, F. Rieutord, Phys. Rev. B 66 (2002) 035402; S. Watanabe, K. Hane,
T. Ohye, M. Ito, T. Goto, J. Vac. Sci. Technol. B 11 (1993) 1774.; C. Bo¨hm, C.
Roths, U. Mu¨ ller, A. Beyer, E. Kubalek, Mater. Sci. Eng. B 24 (1994).
e
0
Topography (left) &
Surface Potential
(right) images of a
CD-RW. SP image
locates the position of
the bits. Courtesy of
Yasudo Ichikawa,
z d ( z d + r0 )
If θ>>0, a more complicated solutions are needed.
Numerical solutions for non-simplified geometries
reported by Watanabe, et al. (1993) and Bohm et al.
(1994) can also be used for the present electrostatic
force calculation.
Ampere A. Tseng, 2010
Nanofabrication Using Atomic Force Microscopy
Magnetic Force Map of
Surface of Zip Disk
Ampere A. Tseng, 2010
AFM: Mechanical Scratching
ƒ Material Removal: Mechanical scratch,
Tunnel Barriers:
Nano-Scale
Modification
AFM Tip
ƒ Material Modification: Anodic oxidation,..
ƒ Nano-Manipulation: Atoms Molecules,
Nanoparticles, nanoclusters…
ƒ M
Material
t i lD
Deposition
iti and
dG
Growth:
th Electrical
El t i l fifieldld
induced mass-transfer, electrochemical
deposition..
Submicro-scale
Modification
Gate
Drain
Source
Gate
ƒ Automation of AFM Nanofabrication
Ampere A. Tseng, 2010
AFM: Mechanical Scratching
* Predictive model
* CNC control with sub-nanometer precision
* Multiple tips
Ampere A. Tseng, 2010
AFM Scratching Versus Oblique Cutting
SEM image of 6
scratched
grooves with
chips in NiFe
substrate using
normal force,
Fn = 1, 2, 3, 5, 7
and 9 µN
AFM scratching
Operation in Contact mode
Triangular pyramid tip
Diamond coated
Ampere A. Tseng, 2010
SEM image of 5
scratched grooves
with chips in NiFe
substrate using
normal force, Fn = 9
µN with number of
scan (No) equal to 1, 3,
5, 7, and 9
Ampere A. Tseng, 2010
4
Finite Element Modeling of AFM Scratching
AFM Scratching of Silicon
Static Model
for normal
AFM tip
(negative
rake angle)
g )
Dynamic
model
For better
tip design
(positive
rake angle)
Ampere A. Tseng, 2010
CORRELATION OF GROOVE DEPTH WITH APPLIED NORMAL FORCE
Color scale: Black
to White is 4.65 nm.
Ampere A. Tseng, 2010
SCRATCHING OF Ni80Fe20 NANOWIRE
Nano-constriction
made by AFM
scratching:
a) original
configuration, b)
after scratching
AFM Scratchability
Al/As2S3
Si
I-V characteristics
and geometric
profile (insert) of
NiFe nanoconstriction
measured: a)
before scratching
(in µA domain), b)
after scratching (in
fA domain).
Ni80Fe
PGMA
Ni
Si
Ampere A. Tseng, 2010
Mechanical Scratching and Etching by AFM
AFM images of V-shaped
grooves on mica substrate
scratched by Si tip at
contact mode: a) 2-nm
deep and 60-nm wide
grooves with one scratch
at normal force of 500 nN,
b) 20-30 nm groove by five
repeated scratches with a
normal force of 5 μN (Tseng
et al., 2007).
Ampere A. Tseng, 2010
AFM Scratching of Au-Pd Film
Depletion of 2-D Electron Gas
(2DEG) of GaAs/AlGaAS heterostructure scratched by AFM-tip with
normal force of 50 μN at scan speed
of 100μm/s: a) measured resistance
against number of scans during
scratching on GaAs/AlGaAs layers,
the inset showing the schematic of
the scanning and measuring
process (Schumacher et al., 1999),
b) Periodic hole arrays in a quantum
well fabricated on InAs/AlSb surface
by direct AFM mechanical
scratching (Rosa et al., 1998).
Ampere A. Tseng, 2010
A Chinese poem (20
characters) of Tang
Dynasty was scratched
on gold-palladium film
(with r.m.s. of 0.2 nm),
which was deposited on
cleaved mica by ion
sputtering. The scratch
was performed by a Si
AFM tip with a force
constant of 35 N/m at a
normal force of 20 μN.
Scratched depth is
about 2 nm.
J. Song, Z. Liu, C. Li, H. Chen, H. He (1998),Appl. Phys. A 66, S715–S717.
Ampere A. Tseng, 2010
5
AFM Local Anodic Oxidation (LAO)
AFM Local Anodic Oxidation
from silicon and metals to complex oxides
Lines induced on Si substrate by AFM using
−8-V DC and 1 m/s scanning speed
• Nanometer-Scale Surface Modification Method
Through Chemical and Physical Interactions between
Tip and Surface
• Anodic Oxidation on the Metal/Semi. Surfaces under
the AFM Tip
• Operation Mode: Contact, Tapping and Noncontact.
AFM Tip
R. Garcia et al. Chem. Soc. Rev. 35, 29–38 (2006)
Si+2h++2(OH-) Æ SiO2+ 2H+ + 2e-
*LAO Patterning: forming
of water memiscus
*Wet etching
… And other metals…. Nb,
Cr, Mo, Al, Ni, Ti, Ta
Ampere A. Tseng, 2010
(a) Silicon oxide dot is
grown below the biased
AFM tip in presence of a
water meniscus. This
dot can be removed by
selective wet etching
leaving corresponding
trenches. AFM
topographic images of
10 nm wide silicon oxide
dots, (b) alternating
insulating and
semiconducting rings ,
and (c) first paragraph
of “Don Quixote” written
by LAO.
Garcia et al. Chem. Soc. Rev. 35, 29, 2006.
Oxidation kinetics involves the
transport of ionic species across the
growing oxide film and subsequent
reaction at one or other of
ambient/oxide and oxide/substrate
interfaces. The process constitutes
reaction and diffusion exhibiting
relaxation-dissipation characteristics.
Æ H2
A. A. Tseng et al., J
Micro/Nanolith.
MEMS MOEMS 84,
043050 (2009)
Bouchiat et al. Appl.
Phys. Lett. 79 123
(2001)
OXIDE DOTS GROWTH BY MULTIPLE PULSES
Oxide dot
label*
1
2
3
4
5
6
7
8
9
10
11
12
Pulse type
static
static
static
modulated
modulated
modulated
modulated
modulated
modulated
modulated
modulated
modulated
Total pulse
duration, T [s]
0.20
1.00
5.00
0.50
1.25
2.50
2.00
5.00
10.0
10.0
25.0
50.0
Half cycle
period, t [s]
0.20
1.00
5.00
0.25
0.25
0.25
1.00
1.00
1.00
5.00
5.00
5.00
Number of
cycles (T/t)
1
1
1
2
5
10
2
5
10
2
5
10
AFM image of twelve oxide dots induced by a
bias of -10 V with 60% humidity under
twelve different pulse conditions.
Ampere A. Tseng, 2010
MODELING OF AFM OXIDATION
(aq) +
2e-
Nb + 4h+ + x OH- Æ Nt
EtchingbOx+ x H+
500 nm
AFM Local Anodic Oxidation (LAO)
2
H+
Ampere A. Tseng, 2010
Development of Wave-Interrogated Near-Field Array
e‐dipole near field << λ/10
Open
waveguide
source
Schematic of Wave Concentration
by a Bowtie Resonant Element
Typical Bowtie Shape
Cabrera − Mott theory (1948) :
During oxidation, OH- diffuse
through material and H+ being
liberated at Si/SiO2 interface:
Si + 4h+ + 2OH– → SiO2 + 2H+
h
dh
= α exp( 0 )
dt
h
Teuschler empirical power law (1995) :
h(t ) = β (V − Vth )t γ
where α , β , γ are cons tan ts
h0 is characteristic decay length
Power Intensity at Free Space λ/8 Below Bowties Supported by BK-7 Superstrate
Ampere A. Tseng, 2010
6
OXIDE BOWTIE INDUCED BY AFM TIP AS ETCHING MASK
AFM Lithography Using Oxidation with SOI Substrate
Si
SOI
(100 nm)
SiO2
SiO2
a) Silicon on Insulator (SOI) Substrate
Single
bowtie
c) Etching of Si using induced
SiO2 as mask
Exposure by scanning AFM
tip
Wave Interrogated
Near-Field Array
(WINFA)
Oxidation is performed on SOI
substrate in which top Si layer is
n-type (0.01 Ω-cm) with (100)
orientation by Soitec. AFM with Si
tip is scanned in contact-mode at
60 nN, 60% ambient humidity, -10
voltages, and 1 µm/s scanning rate.
The etchant used in c) is TMAH at
90 °C. SiO2 etch rate is 2 orders of
magnitude lower than that of
Si(100)
Ampere A. Tseng, 2010
Bowtie
SiO2
SiO2
b) AFM Tip Induced Oxidation
d) Etching of remaining SiO2
Etchant used in c) can
be either potassium
hydroxide (KOH),
tetramethyl ammonium
hydroxide (TMAH) or
hydrazine (N2H4). Using
these echants, SiO2
etch rate is 1 to 2
orders of magnitude
l
lower
than
th Si(100).
Si(100)
Oxidation is performed on
SOI substrate in which the
top Si layer is n-type (0.01 Ωcm) with (100) orientation by
Soitec. AFM with Si tip is
scanned in contact-mode at
60 nN, 60% ambient humidity,
-10 voltages, and 1 µm/s
scanning rate.
Ampere A. Tseng, 2010
Direct patterning of GaAs
I. Local oxidation of Gallium Arsenide
Fabricating tailored quantum devices
high mobility two-dimensional electron gas (2DEG)
below sample surface
Ishii et al., Jpn. J. Appl. Phys. 34, 1329 (1
Matsumoto et al., APL 68, 34 (1996)
Held et al., APL 73, 262 (1998)
Oxidation of GaAs: reproducibility
Insulators Transparent electronics
Strain electronics
ZnO
SrTiO3
MgO
LaAlO3
Al2O3
V2O3
TiO2
VO2
SnO2
Ca1-xSrxVO3
In2O3:Sn
Superconductivity
YBa2Cu3O7-x
Epitaxial growth of functional oxides
La2-xSrxCuO4
Multiferroics
Ferroelectrics
Pb(Zr,Ti)O3
BaTiO3
Spin electronics
Fe3O4
(LaSr)MnO3
LaFeO3
La1-xSr1+xMnO4
Metal &
Semiconductors
BiMnO3
Thermoelectrics
SrRuO3
LaCoO3
(La,Sr)TiO3
NaxCo2O4
BiFeO3
SrTiO3-x
7
Patterning TMOs Thin Crystalline Films
Fabrication of Insulating Barriers & Nanocircuits on Oxides
(Transition metal oxides)
E-beam and Dry Etching
Focused Ion Beam (FIB)
La0.7Sr0.3MnO3
High energy
processes !!!
16μm x 16 μm
15μm x 15 μm
FIB damage of
oxide thin
films
I. Pallecchi et al. Journal of Magnetism
and Magnetic Materials 320 1945–1951
(2008)
Surface
S
f
d
damages off
oxide substrates
T. Arnal et al. Microelectronic
Engineering
La 78–79
Sr 201–205
MnO (2005)
2/3
1/3
(La,Pr,Ca)MnO3 Nanochannels
Ch
Charge
modulation
d l ti on
(La,Sr)MnO
La,Sr)MnO3 channels
SrTiO3-δ thin film side
gate transistors
3
Advantages of using AFM lithography …
• High contrast imaging and precise positioning on any kind of surface
• Low energy processes (absence of lateral damages)
• No Vacuum processes needed
• Very high resolution can be achieved
Y. Yanagisawa et al. J. Appl.
Phys. 100, 124316 (2006)
Why patterning crystalline Transition Metal Oxide (TMO) films
IPallecchi et al. PRB 71, 014406 (2005)
a) Studying different
substrate materials
and oxide
composition.
b) Studying oxide
growth mechanism
and effects of
applied DC voltage,
d
duration
i time,
i
relative
l i
humidity, & pressure
on oxide thickness.
c) Comparison of stamp
roughness and
oxides roughness at
different applied DC
voltage, duration time,
relative humidity, &
pressure.
V
Drain
• Nanosized TMO can be employed for the
fabrication of functional nanodevices
(Nanogaps, ferromagnetic nanoelectrodes
for molecular electronics)
Source
Gate
• Fabrication of nanochannels and
functional devices (spin devices, field
effect devices)
Ampere A. Tseng, 2010
Imprint Local Anodic Oxidation (ILAO)
Source
• Physical properties of many TMOs are
inhomogeneous at nanoscale Æ studying
size effects and phase separation in
TMOs (nanowires)
L. Pellegrino, at al. Appl. Phys.
Lett. 81, 3849 (2002)
Gate
Drai
n
• Thin film templates (nanodots, grids,
interdigital circuits)
Ampere A. Tseng, 2010
Comparison of AFM LAO & Imprint LAO
a) AFM images and
corresponding cross sections
of oxide features obtained on
ZrN thin film as they go
through the sequence of AFM
oxidation, HF and TMAH
etching from top to bottom.
b) Schematic representation of
the sequence of oxidation, HF
and TMAH etching processing
steps.
c) AFM images and
corresponding cross sections
of oxide patterns obtained on
ZrN (using a silicon stamp
with posts) as they go
through the sequence of
Imprint oxidation, HF and
TMAH etching from top to
bottom. (Farkas et al., 2010 in JNN)
Quantum ring coupled to quantum dot
Lithography on 8nm Ti top gates:
7 gates
7 degrees of
freedom
Martin Sigrist, Andreas Fuhrer
Ampere A. Tseng, 2010
8
AFM Tip Induced Deposition
Electrochemical deposition (ECD)
Gold Nanowire Made by Tip Induced Deposition
Electric field-induced mass transfer (EFTM)
In ECD, the tip and
substrate act as two
electrodes to form a
nanoscale electrochemical
cell to perform a chemical
reaction.
AFM images of electrochemically
induced carbonaceous mounds and
lines on Au surface: a) mounds with a
height increasing from 4 nm to 11 nm
produced over a sweeping voltage
varying from -4 to -12V, b) lines with a
height increasing from 3 nm to 15 nm
produced by a voltage varying from -4
V to -8 V.
B. M. Kim et al., Jpn. J. Appl. Phys. Part 1, 40, 4340, 2001. Ampere A. Tseng, 2010
Brushes Grafted by Photopolymerization
Using Thiol-Based Iniferters on Au Nanowire
a) A gold-coated tip is operated at oscillating noncontact mode onSi (100) surface with 2-nm native
oxide, b) a voltage of 10-15 V with 0.5-5.0 ms pulse
is loaded to produce the gold transport from the tip
to surface.
M. Calleja et al., 2001 appl. Phys Lett
* To prevent the formation of local silicon
oxides, the sample is biased negatively with
respect to tip.
a) AFM image of a gold nanowire on a
* Each voltage pulse produces a gold dot on
4.3 nm oxide film, which was formed by
the insulating (oxide) surface and nanowire
the application of pulses of 5 ms at -18 V.
consists of a succession of gold dots which
b) I –V characteristics of the nanowire is
separations are smaller than their diameter.
obtained at room temperature.
Ampere A. Tseng, 2010
Nano-xerography: Patterning by Deposited Charges
a) & b) gold
nanowires asembled
on hydrideterminated Si using
AFM tip with
HAuCl4 coating
c) & d) UV-initiated
photopolymerization of
PMMA brushes
using thiol-based
iniferters (DTCA)
assembled on Au
nanowire platform
Ampere A. Tseng, 2010
Nanomanipulation
Lateral Manipulation
Nano-xerography
(a) Charge patterns are written into an electret layer on a solid
substrate by applying voltage pulses to a conductive AFM tip. (b)
The sample is developed in a suspension of nano-objects. (c)
After rinsing and drying, the nano-objects remain selectively
attached to the predefined pattern.
A Stemmer, D Ziegler, L Seemann, J Rychen N Naujoks,J. Physics: Conference Series 142, 012048 (2008)
Vertical manipulation
Ampere A. Tseng, 2010
Nanoscale
Manipulation
(Bottom-up)
Forces
8
Push Objects
4
6
4
2
1
0
0
-2
AFM images of lateral manipulation of
24-nm Au nanoparticles to create
chain-like nanostructure by FM-AFM: a)
pushing nanoparticles labeled with 2
and 3 along direction shown by arrows,
b) nanoparticles 2 and 3 are pushed
close to nanoparticle 1, c) moving
nanoparticle 4 towards nanoparticle 1,
d) final chain-like nanostructure
(A. A. Tseng and Z. Li, J. Nanosci. Nanotech., 2007)
Adatom remains bound to
surface and pushed or dragged
by tip: a) pulling where adatom
discontinuously follows tip
from one adsorption site to
another due to attractive forces,
b) sliding where adatom is
trapped under tip and follows
its motion instantaneously and
continuously, c) tip is retracted
at desired place.
Adatom is transferred from
surface to STM tip and back
to surface: a) tip picking
adatom from adsorption site
and adatom dissociation
occurring, b) tip lifting
adatom from surface and
moving to desired place due
to attractive forces, c) tip
with adatom is loaded at
desired site.
Ampere A. Tseng, 2010
-4
Lift-Drop
3
500
6
1000
1500
2
Time (msec)
2000
2500
3000
5
-6
1
6
2
5
3
4
Ampere A. Tseng, 2010
9
ATOMIC AND MOLECULAR MANIPULATION
How to Move an Atom
STM image of atomic manipulation of
iron atoms on copper(111) surface in
writing Chinese characters for "atom”
by C. P. Lutz and D. M. Eigler, to
which the literal translation is
something like "original child" (courtesy
of IBM Research, Almaden Research Center)
STM image of nanoscale millennial
numbers “2000” are constructed
with 47 CO-molecules regulated on
a Cu(211) surface using lateral
manipulation at 15 K (courtesy of Dr.
Gerhard Meyer of IBM Zurich Research Laboratory,
Rüschlikon, Switzerland).
Ampere A. Tseng, 2010
In e, silicon, tin
and hydrogen
atoms are
represented by
yellow, blue and
white spheres,
respectively,
and the tip apex
and surface
models
correspond to
the atomic
arrangements
in the upper
and lower
halves
respectively.
a) By gently exploring the repulsive forces of the bonding interaction between the foremost atom of the AFM tip
and atoms probed at a surface, it is possible to induce the vertical interchange of the interacting atoms. Here, a
Si defect of the Sn/Si(111)-(3x3)R30° surface (white circle) was replaced by a Sn atom coming from the AFM tip.
In a subsequent process, the newly deposited Sn atom (dark circle) was substituted by a Si atom coming from
the tip. Applying this manipulation method in heterogeneous semiconductor surfaces enables one to 'write' (b)
and 'erase' (c) atomic markers by respectively depositing and removing the atoms in lower concentration (Si in
the case of b and c). Reproducibility of this manipulation method provides another way to create atomic designs
on surfaces with an AFM at room temperature (d). These vertical-interchange manipulations involve complex
multi-atom contacts between tip and surface.
Ampere A. Tseng, 2010
(Custance et al., Nature Nanotechnology 2009).
MOLECULAR DYNAMICS SIMULATION
“Atom Inlay”, that is, atom letters ”Sn” consisted of
19 Sn atoms embedded in Ge(111)-c(2 × 8) substrate
Sugimoto et al. Nature Mater. 4, 156-159, 2005
Schematic models of lateral atom manipulation
(a) IBM group (STM low temperature), (b) Hitachi
group (AFM low temperature), and (c) Osaka
group (AFM room temperature).
Ampere A. Tseng, 2010
AFM Operation In Dynamic Mode
(a), and of the onset of the chemical
bonding between the outermost tip
atom and a surface atom (highlighted
by the green stick) that gives rise to
the atomic contrast (b). However, the
tip experiences not only the shortrange force associated with this
chemical interaction, but also longrange force contributions that arise
from van der Waals and electrostatic
interactions between tip and surface
(though the effect of the latter is
usually
ll minimized
i i i d through
th
h
appropriate choice of the
experimental set-up). c) Curves
obtained with analytical expressions
for the van der Waals force, the shortrange chemical interaction force, and
the total force to illustrate their
dependence on the absolute tip–
surface distance.
d–e), Dynamic force microscopy topographic images of a single-atomic layer of Sn (d) and Pb (e) grown,
respectively, over a Si(111) substrate. At these surfaces, a small concentration of substitutional Si defects,
characterized by a diminished topographic contrast, is usually found. The green arrows indicate atomic
positions where force spectroscopic measurements were performed. Image dimensions are
(4.3 4.3) nm2; for the acquisition parameters (Sugimoto et al., Nature 2007).
Ampere A. Tseng, 2010
What Is Dip-Pen Nanolithography (DPN)
In DPN, the cantilevered tip is coated with a thin film of ink molecules that can
react with the substrate surface to create a chemical or biological reaction,
which can be controlled at the nanoscale level.
A scene from a molecular dynamics simulation of an atomic force microscope. Here
a hard nickel tip comes down to a soft gold substrate. Before the tip can touch, the
surface gold atoms jump up and coat the tip, leaving a neck of gold joining the
surface with the tip. Elongation of the atomic spheres and spot coloring are used to
indicate elongation/compressive and shear forces.
Ampere A. Tseng, 2010
The tip in DPN is not only used for energy transfer to substrate surfaces as it does in AFM
but also used for coating material transfer for further chemical or biological reactions
Ampere A. Tseng, 2010
10
Dip-Pen Nanolithography (DPN)
a) Schematic showing the generation of CdS
features through the simultaneous reaction of ink
precursors, b) AFM morphology image of CdS
patterns created (Ding et al., 2005)
d) AFM image of Cu nanowires fabricated with DPN, in
which ascorbic acid was dropped onto freshly cleaved mica
first, and then writing on the mica with AFM tip adsorbed
with CuSO4 molecules (Tseng and Li, 2007).
Ampere A. Tseng, 2010
Biological-based
Nanostructures by DPN
Mesa-like nanostructure
of BSA (bovine serum
albumin) on mica
surface written with tip
contact force of 5 nN: a)
AFM image, b) crosssection profile along the
black line shown in a).
R6G (rhodamine 6G,
organic dyes)
nanostructures
written on mica
surface with tip
writing speed of: a)
0.01 μm/s, b) 0.04
μm/s.
(A. A. Tseng and Z. Li, J. Nanosci. Nanotech., 2007)
Detection of HIV-1 p24 antigen using a nanoarray of anti-p24
antibody: a) DPN-generated nanoarrays of MHA are used to
immobilize anti-p24 antibodies on a Au substrate. The bare Au
regions were passivated with 11-mercaptoundecyl-tri(ethylene
glycol) (PEG), and nonspecific protein adsorption was minimized
by blocking with bovine serum albumin (BSA). The presence of
HIV-1 p24 in patient plasma is probed by measuring the height
profile of the anti-p24 antibody array. The height increase signal
as a result of specific antigen–antibody binding is further
amplified by a nanoparticle sandwich assay. b–d, AFM images
that demonstrate the detection of HIV-1 p24 antigen. b) Anti-p24
IgG protein nanoarray. Topography trace of adsorbed anti-p24
IgG on MHA. C) After p24 binding to anti-p24 IgG, a height
increase for the IgG features is observed. d, p24 detection after
amplification with anti-p24 IgG coated gold nanoparticles (20
nm) (courtesy of C. A. Mirkin of Northwestern Uni)
Ampere A. Tseng, 2010
DIP-PEN NANOLITHOGRAPHY (DPN)
DPN Multiple Tips & Parallel Processing
Nanofountain pen: a) Schematic of writing mechanism of DPN probe, where molecular ink
fed from reservoir forms liquid-air interface at annular aperture of volcano tip, b) ink from
reservoir is delivered to the tip via capillary forces, c) SEM image of volcano tip, d) SEM
image of volcano dispensing system (courtesy of C. A. Mirkin of Northwestern University)
Nanostructures fabricated by DPN using 55,000 pyramidal tips: a) SEM image of
part of a 2D 55,000-tip array, b) AFM image of miniaturized replica of five-cent coin
generated by depositing 1-octadecanethiol on gold-on-SiOx substrate followed
with wet etching, where background is optical image of representative region of
the substrate on which approximately 55,000 duplicates were generated (courtesy
of C. A. Mirkin of Northwestern University).
Ampere A. Tseng, 2010
Scanning Near-field Optical Microscopy (SNOM)
In SNOM, the cantilevered tip is used as a nanoscale light source/collector or as
a scatterer. Because the distance between the probe and the sample surface is
much smaller than the wavelength of the light source, SNOM works in "nearfield" and the optical excitation of materials at spatial resolutions is well below
the far-field diffraction limit.
A wide variety of
induced energy
sources, including
electrostatic, optical,
optochemical
optochemical,
optoelectrical,
optomagnetic,
mechanical and
thermal have been
adopted by SNOMbased techniques, to
enhance its capability.
a) aperture SNOM,
b) apertureless SNOM
Ampere A. Tseng, 2010
Material Oxidation by SNOML
AFM images of three oxide patterns on Si substrate generated
by NSOM: a) with optical illumination at intermediate
oscillation amplitude, b) no illumination at relatively low
oscillation amplitude, and c) no illumination at high oscillation
amplitude, with all other parameters held constant
(courtesy of Matthew B. Johnson of University of Oklahoma)
Tseng, 2007 Optics & Lasers Eng.
Ampere A. Tseng, 2010
Ampere A. Tseng, 2010
11
Material Removal by SNOML (Ablation)
Nanoholes in
anthracene crystal film
by ballistic ablation
through SNOM
radiation; the shear
force topographic
image is shown in the
top figure, while the
profile measurement is
plotted below (courtesy
of Renato Zenobi of
Swiss Federal Institute
of Technology).
Material Deposition by SNOML
Two Zn nanodots deposited on glass substrate by SNOM
photodissociation of precursor diethylzinc gas: a) shearforce image, (b) the cross-sectional profile taken along the
white dashed line in Panel (a) (after Yamamoto et al., 2000).
Ampere A. Tseng, 2010
Material Modification by SNOML
Ampere A. Tseng, 2010
Equipment to Have Precision Of ~1 nm
• Develop closed-loop control strategy to reduce the
geometric errors induced by equipment including
hysteresis creep by piezo scanner, AFM tip, mechanical
drift, thermal drift…,
- To reduce the hysteresis creep, feedback signal uses
direct-measuring,
direct
measuring non-contact
non contact capacitive position sensors
(high motion linearity, long-term stability, phase fidelity)
- To reduce mechanical drift, positioning and scanning use
frictionless flexure guidance (within 0.01 nm/s)
Photopatterning of nanostructure in SAM: a) 3 major steps for
photopatterning: SNOM selective exposure, photooxidation of exposed
region, and contrasting thiol replacing oxidized region, b) FFM image of a
39-nm wide line of dodecanethiol written into SAM of mercaptoundecanoic
acid, c) five ~40-nm wide lines of mercaptoundecanoic acid written into
dodecanethiol by reversed procedure (courtesy of Graham J. Leggett of
University of Sheffield).
- To reduce thermal drift, invar or low thermal expansion
materials is used for the stage (within 0.01 nm/s)
- The total inaccuracy should be less than 1 nm/mm and
0.01 nm/s.
Ampere A. Tseng, 2010
DESIGN SOFTWARE FOR PRECISION PARTERNING
• Dimension and accuracy of patterns are highly affected
by operating parameters: contact mode, tip material,
scanning speed, humidity, applied voltage….
• Accuracy of patterning scheme requires further refining,
and better processing procedures need to be developed.
• Height and width modulation by adjusting the phase and
the duration time of pulsed voltage (short pulse voltage
restricting lateral diffusion while high voltage pulse
producing fast growing in height).
• Develop CAD software for the design and control of
AFM (including DPN, STM, SNOM) oxidation and
scratching patterning.
Nano- and Macro-Integrated Manufacturing
Desk Top Based System
Manufacturing
Execution System
Vehicle &
Stocker
C t ll
Controllers
Material Handling
Equipment
Station
Prod. Equipment Controllers
Execution
Control
Material
Control
System
APC
View Dispatch Lists
Move
Queue
Dispatch
Job Control/Trigger
Wafer
control
SPC
Real-time
Scheduler/
Dispatcher
Decision Support Systems
Ampere A. Tseng, 2010
12
Parallel Processing & Multi-Resolution
(IBM Millipede and Special Tip Design)
Schematics and SEM
image of a cantileverSWNT-based sensing
device. The white
arrows indicate the
location of the
suspended SWCNT.
Deflections of the
cantilever induce
strains in the CNT
leading to a change in
its resistivity
(Stampfer et al.,
2006).
Millipede chip: the electrical wiring
for addressing the 1,024 tips etched
out in a square of 3mm by 3mm (The
chip's size is 7 mm by 14 mm
http://domino.research.ibm.com/Comm/bios.nsf/pages/millipede.html
Parallel Processing of AFM Tip Arrays
A key element when developing probe array devices is a convenient
read-out system for measurements of the probe deflection. Such a readout should be sufficiently sensitive, resistant to the working
environment, and compatible with the operation of large number of
probes working in parallel.
Schematic of three main classes of sensory used for deflection detection in
AFM
1) external sensor: sensor is not
integrated in the cantilever,
2) self sensing: sensor is integrated in
the cantilever,
3) Tip-surface interaction sensor:
other tip-surface than force
interactions are detected, e. g.
thermal or electrochemical
interactions (Courtesy of J. PoleselMaris).
Ampere A. Tseng, 2010
Capacitive Devices for AFM Tip Sensing and Actuating
a) SEM image of array of
mircofabricated capacitive
cantilever sensors, b) and c)
enlarged view of cantilever ends,
showing the gap between
cantilever counter-electrode as
well the tip. The perforation of
cantilever promotes the removal
of SiO2 between the cantilever
and the counter-electrode.
Sensing and Actuating for Arrays of AFM Tip
Ampere A. Tseng, 2010
Other Applications Using Atomic
Force Microscope
Schematic of AFM Capacitive Sensor and
Actuator (Brook et al., 2003)
Schematic of AFM with integrated
g
p
piezoresistive sensor and p
piezoelectric
ZnO actuator. The cantilever is divided into a actuator and sensor region
(Minne et al., 1998).
Ampere A. Tseng, 2010
AFM DESK TOP NAMOFABRICATION
TIP BASED DIRECT
WRITING
PROTOTYPING
Ampere A. Tseng, 2010
Roadmap for Tip-Based Nanofabrication*
Developed in 2007 for Commercialization
Metric
Feature Position Accuracy
[nm]
Feature Size Variation
[% of dimension]
Heterogeneity in Parameter:
Size Shape,
Size,
Shape or Orientation
2010
50
2012
25
2014
5
10
3
1
Two values of
one parameter
1/min
Feature Fabrication Rate
Single tip
(No. of structure/min/tip with
array tips)
Height < 10%,
Tip Shape Variation
Radius < 20%
[% of dimension with
100 operations
required operations]
In-situ Tip Height Sensing
20
[nm]
Ampere A. Tseng, 2010
Five values of
Continuous
two parameters control over two
parameters
5/min/tip
60/min/tip
Five-tip array Thirty-tip array
Height < 5%,
Radius < 10%
1000 operations
10
* A. A. Tseng, S. Jou, A. Notargiacomo, T. P. Chen, J. Nanosci. Nanotech., May 2008
Height < 1%,
Radius < 3%
106 operations
2
Ampere A. Tseng, 2010
13
For All of Us in Nano Worlds
Life Is Limited! Learning
Is Unlimited!
Nanorization Is Unlimited!
Prospective Applications
Are Unlimited!
Thank You!!
Nanofabrication Using Atomic Force
Microscopes
Atomic force microscopy (AFM) has been used as a
nanofabrication tool for localized material deposition,
removal, and modification for near two decades. The
recent development of several AFM-based techniques will
be introduced with the emphasis on their abilities in
creating a variety of nanoscale components and devices.
Th nanostructures made
The
d by
b these
h
techniques,
h i
especially
i ll
the techniques of mechanical scratching, local anodic
oxidation, and deposition are presented to illustrate the
characteristics and uniqueness of their versatility and
advancement. Recommendations for future research in making
the AFM-based techniques more controllable and in widening
their applicability in nanofabrication are also addressed.
IBM AFM Moving Individual Atoms: www.youtube.com/watch?v=YcqvJI8J6Lc&NR=1&feature=fvwp
Nano, the next dimension, for EU(27:04 min): www.youtube.com/watch?v=eCpkq_AeX50&NR=1&feature=fvwp
Ampere A. Tseng, 2010
Ampere A. Tseng Bio
Ampere A. Tseng is a Professor of Engineering at Arizona State University (ASU).
He received his Ph.D. in Mechanical Engineering from Georgia Institute of
Technology in 1978 and has published more than two hundred fifty referred papers
with nine US patents under his credentials. Dr. Tseng has edited more than ten
technical monographs and has been an editor for more than ten different technical
journals. Professor Tseng was a recipient of the Superior Performance Award of
Martin Marietta Laboratories, RCA Service Award, Alcoa Foundation Research
Award, and ASU 1999-2000 Faculty Award. He chaired the ASME Materials
Division in 1991-1992 and was selected as an ASME fellow in 1995. Also, he chaired
the 2000 NSF Workshop on Manufacturing of MEMS and 1st International
Workshop on Tip-Based Nanofabrication in 2008 as well as he co-chaired 1992
International Conference on Transport Phenomena in Processing and the 1999 NSF
USA-China Workshop on Advanced Machine Tool Research. Dr. Tseng has received
more than three million dollars in research funding directly from government
agencies and industries. In 1990, Professor Tseng managed to secure twelve million
dollars from US Department of Energy to establish Center for Automation
Technology and became its first center director at Drexel University. From 1996 to
2001, Dr. Tseng was the founding Director of the Manufacturing Institute at ASU
and the nine million dollars' donation from Motorola to Manufacturing Institute in
1997 was the largest single gift in ASU history.
Ampere A. Tseng, 2010
14