Download - The Orion Helium Ion Microscope
Nanofabrication of Plasmonic Devices in
the Helium Ion Microscope
Advanced Materials
Characterization Workshop
UIUC
7 June, 2012
Larry Scipioni
Carl Zeiss Microscopy
•Stanford University, Stanford, CA
•Carl Zeiss Microscopy
•Argonne National Labs
•INA, Zaragoza, Spain
Content
•Nano-Apertures
•The helium ion micrscope (HIM)
•Nano-Atennae
1. Nano-Apertures
Optics with diffraction limit
Spot size ~ λ/2 ~ 150 nm
@ λ = 257 nm
1X demagnification system
with negligible aberration
D. S. Pickard et al., JVST. B. (2003)
Motivation: Multiple E-beam Lithography
Increase production throughput with multiple beams
Motivation – Nanoscale Photoelectron
Sources
1. Focus light to the near-field with a nanophotonic structure:
C-aperture with sub-100 nm dimensions
2. Near-field locally excites photoelectrons in a photocathode
(CsBr)
3. Extract photoelectrons with a negative bias voltage
This unit can be
duplicated in an array
for multiple beam sources
(not to scale)
C-Aperture Properties
< 100 nm
1. Small gap/ridge
-- small radiation source
2. Sharp edges
-- good charge concentrationSmall spot requires:
+-
Induced surface current
concentrates charges at the ridge
2.2 α
ααα
α
C-Aperture – Resonance Conditions
Target : 20 nm spot
→ try α = 20 nm
λ=257 nm
(CsBr has a strong
absorption at 257 nm)
J. A. Matteo et al., Appl. Phys. Lett. (2004)
experiments
FDTD
simulations α=40n
m
α=55n
m
T
Aperture Size, α (nm)
Reso
nan
t W
avele
ng
th, λ
(nm
)
Tra
nsm
issio
n (
ct.
/sec.)
Wavelength (nm)
Al80nmAl90nm
Al100nm
simulation
experiment
α=40nm
α=55nm
experiment
Fabrication – Conventional FIB Milling
J. B. Leen et al., Opt. Lett. (2008)
FDTD Simulation,
with λ = 980 nm incidence
Through Membrane Milling
(experiment)
Fabrication – Conventional FIB Milling
J. B. Leen et al., Opt. Lett. (2008)
Through Membrane Milling
(FDTD simulation)
Direct Metal Milling
(experiment)
Direct Metal Milling
(FDTD Simulation)
(With λ=980 nm incidence)
Ga FIB: Ion Milling Dynamics
TRIM simulation
30keV Ga+
Point beam
Au substrate
1000 ions incoming
-120
-70
-20
30
80
-120 -70 -20 30 80Z, n
m
Y, nm
SRIM, All Sputtered Atoms
-10
-8
-6
-4
-2
0
2
4
6
8
10
-10 -5 0 5 10Z, n
m
Y, nm
SRIM, Sputtered Atoms Near Ga+ Impact Point
Nanometer-Precision Machining with Helium Ions
“As particle reflection coefficients increase with decreasing energy (and are quite
high for light Ions), reflective scattering (a) collisions near the target surface
contribute increasingly to sputtering.”*
Is sputtering more localized?
*Behrisch and Eckstein, Sputtering by Particle
Bombardment, Topics in Applied Physics 110, Springer-
Verlag GmbH, Heidelberg, 2007.
2. First Commercial Helium Ion Microscope: Orion
ALIS – Atomic Level Ion Source
Provides a high brightness source
capable of sub-nanometer imaging
resolution
Sub-nanometer Probe Size
Asbestos fiber (crocidolite) and carbon
membrane
200nm field of view
35keV beam
Resolution: 0.21 nm
Excellent surface detail as well
Localization of Sputtered Atoms
TRIM simulation
30keV He+
Point beam
Au substrate
1000 ions incoming
SRIM, All Sputtered Atoms
-120
-100
-80
-60
-40
-20
0
20
40
60
80
-60 -40 -20 0 20 40 60 80 100 120
Y, nm
Z, n
m
SRIM, Sputtered Atoms Near He+ Impact Point
-10
-8
-6
-4
-2
0
2
4
6
8
10
-10 -8 -6 -4 -2 0 2 4 6 8 10
Y, nm
Z, n
m
100nm
50nm 40nm 30nm 20nm 10nm
He-ion vs. Ga-ion
Helium Ion FIB Gallium Ion FIB
100nm
100nm
100nm100nm
Direct Metal Milling Through Membrane
Milling
Material: 40 nm thick aluminum (imaged from HIM) Material: gold (imaged from SEM)
80 100 120 1400
50
100
150
200
X (nm)
Ima
ge
In
ten
sity (
arb
. u
nit)
50 nm
Results
Three neighboring C-apertures,
HIM machined
Image of emission spots
Profiles of photo-current (down
the beam, no focusing)
Simulations indicate beam size
at source should be 22 nm
• Needs to be verified
0
20
40
60
80
100
120
140
160
180
x 1
0^4
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
eV
0.65 eV 1.28 eV 1.71 eV 1.82 eV 2.07 eV 2.31 eV
Line width: 10 nm
STEM image
EELS spectrum
from whole
structure
Higher Order Fractal Apertures
Daniel Pickard, NUS
3. Plasmon Coupling in Nano-antennae
Localized surface plasmons (LSP’s) are electron density
oscillations, which are concentrated on the exterior of
nanostructured materials (NSM).
.
Electron Energy Loss Spectrum
Surface and
Bulk Plasmons
Elastic Beam
~ 1.65 - 3.1 eV
750 - 400nm IR UV
Goal
100 nm thick single crystal Au membrane
Ga ion beams introduce significant damage to thin films. The
resulting stress causes films to buckle. Milled feature size limited
to ~ 50+ nm
Fabrication with Gallium FIB
He Ion Milling: Low Lateral Damage
Nestor Zaluzec, ANL
4 nm
We were able to visualize and measure coupling of the low
energy loss surface plasmons modes ( 0.8 - 3 eV ) of
coupled nanostructures.
1.65 - 3.1 eV <-> 750 - 400nm
Plasmons Observed: STEM-EELS
Conclusions
•Use new beam technology to make newer
beam sources
•Helium-ion FIB uniquely able to mill sub-20
nm C-apertures.
•Photoelectron emission with good
brightness measured
Acknowledgements
Stanford University
Prof. Piero A. Pianetta
Richard C. Tiberio, Paul Rissman, James Conway
Paul C. Hansen and Yin Yuen (Hesselink Lab)
Carl Zeiss, NTS
Chuong Huynh, David Ferranti, Bill Thompson
Funding Support:
DARPA grant TXFEL 1138606-1
Argonne National Labs and INA
Nestor J. Zaluzec, Dean J.Miller, Jon M. Hiller, and Raul Arenal