Helium Ion Microscopy – Extending the Frontiers of Nanotechnology
Giulio Lamedica
Assing SpA / Zeiss Microscopy
Nanofabrication
Why He ions for Imaging?
HeiM on Graphene
Summary
•
•
•
Orion NanoFab Technology•
Conclusions•
Introduction•
More Applications•
Nanofabrication
Why He ions for Imaging?
HeiM on Graphene
Summary
•
•
•
Orion NanoFAab technology•
Conclusions•
Introduction•
More Applications•
4
As the beam is raster scanned across the sample, secondary electrons are generated which are detected by ET Detector ….
Image Formation
HIM Image
BSPB
SE1 SE2
SE3
Pole piece
Resolution in CPM
BSP
Probe Size Interaction VolumeSE1/SE2)
Nanofabrication
Why He ions for Imaging?
HeiM on Graphene
Summary
•
•
•
Orion NanoFAab technology•
Conclusions•
Introduction•
More Applications•
7
Superposition of the aberration discs
0 0.2 0.4 0.6 0.8 1 1.2 1.4
0
1
2
3
4
5
6
7
8
9
10
Resolution and Probe Size – Electron Beam
Probe Size:
35.0 iSS Cd Spherical aberration:
iCC U
UCd
Chromatic aberration:
idd
6.0Diffraction Error:
Demagnified source: gSo dMd
ai ai [mrad]
d p [n
m]
2222dCSgP ddddMd
10.04.2023Page 8
Carl Zeiss NTS, Peter Gnauck
1,00E-06
1,00E-04
1,00E-02
1,00E+00
1 10 100 1000
U [kV]
Wav
elen
gth
[n
m]
Resolution and Probe Size
He+
Ga+
e-
9
0 0.2 0.4 0.6 0.8 1 1.2 1.4
0
1
2
3
4
5
6
7
8
9
10
Resolution and Probe Size – Helium Ion Beam
Probe Size: 2222dCSgP ddddMd
35.0 iSS Cd Spherical aberration:
iCC U
UCd
Chromatic aberration:
idd
6.0Diffraction Error:
Demagnified source: gSo dMd
a
ai [mrad]d p
[nm
]
• The Helium Ion Microscope has a half angle (a/2) of 0.5mrad compared to a typical SEM of 5-10mrad
• The Helium Ion Microscope has a theoretical probe size of 0.2nm and a demonstrated probe size of 0.24nm (product specification <0.35nm)
No diffraction limitations (MHe/Me = 7289)
Helium ions are more particle-like in nature due to higher mass (compared to electrons)
1
Key Attributes of Helium Ion Microscopy
10
He ions have extremely little diffraction effects
Imaging of small aperture with He ions
Imaging of small aperture with He ions
Diffraction limited image
No diffraction limitations
Electron Beam
He ion beamWavelength ~ 0.01 nm
Wavelength ~ 0.0001 nm
MHe/Me = 7289
80X smaller at all energies
221
1
2cm
eUeUm
h
He
He
Key Attributes of Helium Ion Microscopy
11
Spot size = 0.8 nm
Electrons
Very high lateral resolution in images
Sub-nm probe size and very narrow interaction volume
2He ions
Silicon Sample30 nm
1 keV e-beam into Silicon: Image
suffers from large interaction
volume at the surface. Many
SE’s are really SE2.
30 keV Helium into Silicon:
Beam is well collimated
beyond the SE escape depth.
Recoil contribution is
negligible.
Spot size = 0.35 nm
Key Attributes of Helium Ion Microscopy
12
Surface sensitive imaging
Secondary electrons get generated from within 3-5 nm of the sample surface
3Electrons He ions
Silicon Sample30 nm
1 keV e-beam into Silicon: Image
suffers from large interaction
volume at the surface. Many
SE’s are really SE2.
30 keV Helium into Silicon:
Beam is well collimated
beyond the SE escape depth.
Recoil contribution is
negligible.
Sec
on
dar
y el
ectr
on
es
cap
e d
epth
Volume from which SE’s are generated
Volume from which SE’s are generated
High SE yield means low ion doses can generate excellent images
Helium ions generate many secondary electrons per ion
4
Key Attributes of Helium Ion Microscopy
13
Electrons He ions
Silicon Sample30 nm
He ions product 4-7 times as
many secondary electrons
30 keV Helium into Silicon:
Beam is well collimated
beyond the SE escape depth.
Recoil contribution is
negligible.
Key Attributes of Helium Ion Microscopy
14
Electrons
5X-10X greater depth of focus in the images
Helium ion beam has 5X lower convergence angle than FESEM
5He ions
Silicon Sample30 nm
Convergence Angle = 0.020
a
Best Focus
Best Focus
Key Attributes of Helium Ion Microscopy
15
Extremely easy to get high resolution images of insulating samples without complex preparation
Insulating samples are only positively charged under helium ion beam
6
The sample interaction volumes and the positive and negative charge distributions (+,-) arising from imaging with the SEM and with the HIM. SE1 are secondary electrons
created from the primary beam. SE2 are secondary electrons created from backscattered electrons (BSE)
0 nm
10 nm
300 nm
Helium @ 30 kVSEM @ 0.5 kV
-
SE2SE2
SE1
BSE
---
++++ +
+
SE1
SE1
+++ ++
--
-
- -
Bulk Charging
SurfaceCharging
Positive surface charging only -
easily neutralized by electron flood
gun!
Electrons He ions
Why Helium Ion Microscopy?
Very high lateral resolution in images
Sub-nm probe size and very narrow interaction volume
1
No diffraction limitations
Helium ions are more particle-like nature due to higher mass (compared to electrons)
2
Surface sensitive imaging
Secondary electrons get generated from within 3-5 nm of the sample surface
3
High SE yield means low ion doses can generate excellent images
Helium ions generate many secondary electrons per ion
4
5X-10X greater depth of focus in the images
Helium ion beam has 5X lower convergence angle than FESEM
5
16
Extremely easy to get high resolution images of insulating samples without complex preparation
Insulating samples are only positively charged under helium ion beam
6
Nanofabrication
Why He ions for Imaging?
HeiM on Graphene
Summary
•
•
•
Orion NanoFAab technology•
Conclusions•
Introduction•
More Applications•
What is Ion Beam Milling?
18
Schematic showing material being sputtered away by helium beam
Illustration from “Gas-assisted focused electron beam and ion beam processing and fabrication”, J. Vac. Sci. Technol. B 26(4), Jul/Aug 2008
Helium ion beam can remove material …
(1) … at a controlled rate(2) … with high fidelity(3) … from within 5 nm of beam impact point
Complex shapes and arrays of shapes can be milled using patterning engine.
APPLICATION AREAS
(4) Nanopore fabrication in thin films(5) Precision milling of thin films(6) Optical and magnetic metamaterial research
Ion beam milling utilizes the sputtering capability of ion beam to remove material
Why is Helium Ion Beam Suitable for Nanofabrication?
Remove material by sputtering
Helium ions are much more massive than electrons
1
Remove material at a controlled rate
Helium ions are less massive than gallium ions
2
Remove material locally
Helium ions sputter material from within 5 nm radius of beam impact point
3
Chemically enhanced etching and deposition at length scales not achievable with Gallium FIB
Helium ions can induce etching and deposition reactions at surface with precursor gases4
No proximity effect in helium ion beam lithography
Helium ions scattering profile in resists is narrow conical with low backscatter
5
High sensitivity, better contrast than e-beam lithography
Helium ions can expose resists in 5X smaller doses
619
Ion Beam Milling Comparison between Helium and Gallium FIB
20
1 10 20 30 100 nm
Ga FIBHe FIB
Helium FIB
Type of Ion Source Gas Field Ion Source
Minimum feature size
Spot size (30 kV)
Diameter of sputteredregion in gold (spot)
1 nm
0.35 nm
2.6 nm
Gallium FIB
Liquid Metal Ion Source
25 nm
5 nm
20 nm
Suitable for milling Small structures Large structures
Nanofabrication Examples …
21
Graphene Photonics
DNA Sequencing
Nanopores
Lithography Nanopillars
Nanofabrication
Why He ions for Imaging?
HeiM on Graphene
Summary
•
•
•
Orion NanoFAab technology•
Conclusions•
Introduction•
More Applications•
He Ion Beam MillingGraphene Research
Research Area
Graphene is a flat monolayer of carbon atoms tightly packed into a two-dimensional
(2D) honeycomb lattice, and is a basic building block for graphitic materials. It has
extraordinary properties:
(1) Electronic (2) Optical (3) Thermal (4)
Mechanical
2010 Nobel Prize in Physics awarded for groundbreaking experiments with
graphene
ResearchApplications
Nanoribbons
Transistors
Optical modulators
Integrated circuit
Transparent electrodes
Ultracapacitor
Chemical and electrical sensors
Structure
Helium Ion MicroscopyImaging of Graphene
24
Material Science
Challenge How do you see graphene CVD growth?
Zeiss Solution Helium Ion Microscopy: highly surface sensitive imaging
The grain boundaries of
the graphene can be
identified as ridges on the
surface.
CVD grown graphene
monolayer on copper.
Sample Courtesy: University of Houston
Research
Helium Ion MicroscopyImaging of Graphene
Material Science
Challenge How do you see quality of Graphene trasferred on Silicon ?
Zeiss Solution Helium Ion Microscopy: highly surface sensitive imaging
Research
University of Bielefeld (D)
Helium Ion MicroscopyImaging of Graphene
Graphene Machining for Quantum Confinement
The bandgap in a graphene
ribbon increases as the
ribbon width decreases
In order to increase bandgap
above room temperature
thermal energy (25 meV),
confinement of ribbon to less
than 20 nm is desired.
M. Han, B. Özyilmaz , Y. Zhang., P Kim, Phys; Phys. Rev. Lett. 98 (2007) 206805
Graphene nanoribbons bandgaps can be modulated
Current Solutions
• Lithographic patterning has been applied, but resist deposition and then removal can alter graphene electronic properties.
• Ga FIB milling produces too much damage to be useful (image)
• E-beam bond damage, followed by chemical etch, cannot produce sufficiently sharp feature edges.
• Need: low damage, precise, method that does not touch graphene intended for pattern.
Gierak et al., Microscopy Today (2009)
FOV 500 nm
1.86 E18 1.99 E18
* All units in Ions/cm2
2.39 E18
2.13 E18
2.53 E18
2.93 E18
2.26 E18
2.63 E18 2.79 E185-6 nm width
Direct Patterning of Graphene:5 nm Features
Graphene created by the exfoliation method (1-3 layers thick)
Created on SiO2 over cylindrical holes on surface.
Ion milling carried out on the suspended area.
FOV 100 nm
2.79 E18
Dr. Dan Pickard, National University of Singapore
4.8 E18
2.9 E18
4.8 E18
Dose (ions/cm2)
5nm width
10nm width
20nm width
VerticalFOV 700nm
Direct Patterning of Graphene:Ribbon Width Control
• Pattern generator (Nabity ) used to define milling structures
• External control of column
• 700 nm vertical field of view
• Milling proceeded simultaneously down both sides of ribbon to maintain strength
Dr. Dan Pickard, National University of Singapore
10nm wide ribbon3.5 microns long
20nm wide ribbon3 microns long
Direct Patterning of Graphene
• 20 nm and 10 nm wide suspended ribbons
• 4 µm field of view
• Aspect ratio up to 350X
FOV 4 µm
Dr. Dan Pickard, National University of Singapore
• Graphene layer (could be multiple layers) on SiO2 substrate
• Goal: creation of a quadrupole quantum dots structure
• 4 dots, with 4 electrodes to control the occupancy of dots
• Created by bitmap imported into Orion patterning interface
• 10 nm gaps have been created
• Next required step: pattern electrodes to the device for electrical testing (using beam chemistry!)
Graphene Milling on a Substrate
Creation of features with high machining precision
Graphene on SiO2
Courtesy of Stuart Boden, University of Southampton
Graphene Nanoribbons
Why Helium Ion Milling over other methods?
• Fast
• Non-destructive
• Contamination free
• Extends limitations (down to 5-6 nm width)
• Capable of complex geometries
• External control of column
Nanofabrication
Why He ions for Imaging?
HeiM on Graphene
Summary
•
•
•
Orion NanoFAab technology•
Conclusions•
Introduction•
More Applications…•
Carbon Nanotubes – Large Depth of Focus
200nm
Research Single walled Carbon nanotubes on Si-Ge catalyst imaged with a 70° tilt
Challenge study of the growth dynamics that progress parallel to the substrate in this case
Zeiss Solutionlong depth of focus allows the CNT attachment to the catalyst to be imaged deep into the background Contrast for low atomic weight material at high resolution
Sample courtesy Prof. H.N.Rutt, Univ. of Southampton
Helium Ion MicroscopyCarbon Nanotubes
Research CNT with Sn and Pd nanoparticles
Challenge How do you evaluate nanoparticle distribution?
Zeiss Solution Helium Ion Microscopy: Topographical and Material contrast
Nanowires – Strong Materials Contrast
100nm
Sample courtesy Princeton University
Research Nanowires in the beginning of growth phase Catalyst array in substrate
Challenge Study the dynamics of the growth in this system with greater detail
Zeiss SolutionStrong material contrast clearly delineates the nanowires but without saturation of the image
Helium Ion MicroscopySAM Modification
Research Nitro-biphenyl-thiol (NBPT) self-assembled monolayer on gold, Electron beam patterning via stencil mask converted terminal nitro group to amine
Challenge How to identify chemical changes?
Zeiss SolutionHelium Ion Microscopy: Topographical and Material contrast possible studies of this chemical lithography which otherwise requires AFM, which has throughput limitations
Helium Ion MicroscopyImaging of Uncoated Polymers
39
200 nm 200 nm
SEM HIM
Research Bioengineering (PLLA/hydroxyapatite composites for large bone defect healing)
Challenge How do you visualize biomineral growth on sensitive polymer surfaces?
Zeiss Solution Helium Ion Microscopy: damage –free imaging
Hydroxyapatite
crystal on PLLA
Charging and
sample damage
Research Material Science
Challenge How do you visualize at high magnification low weight materials ?
Zeiss Solution HeIM: Good contrast for low weight materials @ over 1MX (0.29 nm res)
Helium Ion MicroscopyCarbon Black
Helium Ion MicroscopyImaging of Inner Ear Tectorial Membrane
41
Bioscience
Challenge How do you see the complex morphology of tissue nanostructures?
Zeiss Solution Helium Ion Microscopy: charge neutralization technology allows clear view
Sample Courtesy: NIH
Research
Ion Beam MillingMetamaterial Research
42
Research Area
Metamaterials are engineered materials with properties that are not found in natural
materials. Also known as “left-handed” media, “Negative refractive index” media
Metamaterials gain their properties from structure rather than composition, using
small periodic (1D, 2D or 3D) inclusions (holes, lines, space etc.) in bulk material to
create effective macroscopic property.
Electromagnetic WavesVisible lightInfraredTerahertzMicrowavesRadiowaves
ResearchApplications
Terahertz materials
Photonic materials
Plasmonic materials
Metamaterial antennas
Nonlinear materials
Metamaterial absorber
Superlens
Cloaking devices
Working Principle
The objective is to create a “structured” metamaterial that will exhibit desired properties when electromagnetic waves interact with respect to(1) Propagation (3) Absorption(2) Transmission (4) Reflection
Metamaterial
Ion Beam MillingMetamaterial Research
43
TraditionalMethods
Lithography
Layer by Layer or Self-assembly based methods
Zeiss Ion Beam Milling
Solution
Drawbacks Multi-step – have to rely on success of multiple steps
Tedious – numerous iteration of process development steps
Structure is big enough to make with Ga FIB
20 nm Gold (evaporated)5 nm ITOGlass Substrate
Zeiss Ga FIB Solution: Array fabricated in 20 minutes
Source: “Focused-Ion-Beam Nanofabrication of Near-Infrared Magnetic Metamaterials”, Adv. Mater. 2005, 17, 2547–2549
Ion Beam MillingMetamaterial Research
44
Going Smaller By making the shapes in the array smaller, one can modulate the frequency
response of the metamaterial.
Example: As array element is made smaller, transmission of shorter wavelengths is suppressed.
Long wavelengths blocked
Medium wavelengths blocked
Shortwavelengths blocked
How does one makesmaller
structures?
Helium Ion Beam Milling, (Neon Ion Beam Milling)
Ion Beam MillingComplex Shapes for Plasmonics
45
Research Area Plasmonics, Photonics, Sensors
ChallengeHow does one make small enough structure in metal film that will exhibit plasmon-
enhanced transmission at desired wavelength?
Zeiss Solution Helium Ion Beam Milling
Theory: Fractal shapes
enhance plasmon-
assisted transmission*
*Source: “Fractal extensions of near-field aperture shapes for enhanced transmission and resolution”, Optics Express, 2005, 13, 636-647** Courtesy: Dan Pickard, NUS
First fractal iteration based on Hilbert Curve
Second Fractal iteration based on Hilbert Curve
50 nm
Helium ion
beam milling
can make
complex
structures Au Al Ag
**
Ion Beam MillingTechnology Comparison • Ga FIB vs. Helium Ion Beam
46
1 10 20 30 100 nm
Ga FIBHe FIB
* Courtesy: Dan Pickard, NUS
What is Ion Beam Induced Etching?
47
Schematic showing material being etched away by He beam in the
presence of precursor gas molecules
Illustration from “Gas-assisted focused electron beam and ion beam processing and fabrication”, J. Vac. Sci. Technol. B 26(4), Jul/Aug 2008
When an etch gas (such as XeF2) adsorbs on a surface,
enhanced etching/material removal will occur if the
surface is scanned by helium ion beam.
APPLICATION AREAS
(1) Photomask repair
(2) Removal of excessive amounts of material
Material removal in the scanned region
He+
Ion Beam Induced EtchingPhotomask Repair
48
Area Photomasks for lithography
Challenge How do you increase throughput in EUV photomask repair?
Zeiss Solution Helium Ion Beam Induced Etching
TaN Absorber Layer
No XeF2 XeF2 Present
TaN Absorber Layer
12 nm wide lines at 25 nm
pitch
Etching speed significantly
enhanced by XeF2 precursor
Same exposure conditions
(areal dose / scan repeats etc.)
Introduce XeF2
100 nm
Source: Diederik Maas, TNO
What is Ion Beam Induced Deposition?
49
Schematic showing material being deposited by He beam in the presence of
precursor gas molecules
Illustration from “Gas-assisted focused electron beam and ion beam processing and fabrication”, J. Vac. Sci. Technol. B 26(4), Jul/Aug 2008
When a deposition precursor gas adsorbs on a surface,
material will be deposited if the surface is scanned by
helium ion beam.
APPLICATION AREAS
(1) Deposition of conductive lines and pads
(2) Failure analysis of integrated chips
Material deposition in the scanned region
He+
Ion Beam Induced DepositionApplication • Vertical Nanopillars
50
Area AFM probes tips, Hard mask for lithography
Challenge How does one create vertical nanopillars?
Zeiss Solution Helium Ion Beam Induced Deposition
Platinum Nanopillars
(a) At low currents
(b) Blow-up of the
enclosed pillar, the
yellow ellipse is the
estimated pillar
bottom
(c) At high currents
Source: Nanotechnology 21 (2010) 455302 (7pp)
What is Ion Beam Lithography?
51
When resists such as HSQ and PMMA are
exposed to ion beams, their solubility
changes and can be used for patterning.
Just like electron beams, ion beams can be used for lithography
He+
He+
Develop
Develop
Ion Beam LithographySub-10 nm Lithography
52
Research Area
There is an interest in making smaller and smaller lines at a tighter pitch using
lithography to keep up with Moore’s law.
State-of-the-artE-Beam Litho Best results : 6 nm lines at 12 nm pitch
Half-pitch = 5 nmDose = 4000 e-/nm
Half-pitch = 6 nmDose = 4400 e-/nm
Half-pitch = 8 nmDose = 5000 e-/nm
Half-pitch = 10 nmDose = 6300 e-/nm
Source: Karl Berggren, MIT
Reaching limits of EBL ….
Ion Beam LithographySub-10 nm Lithography
55
Ion Beam LithographyNeon Beam Lithography
56
Nanofabrication
Why He ions for Imaging?
HeiM on Graphene
Summary
•
•
•
Orion NanoFab Technology•
Conclusions•
Introduction•
More Applications•
58
Orion Plus
He – Ne Gas Field Ion Source (GFIS)Single column – dual source concept
Probe Size; Probe Current:
He – 0.5 nm; 0.1 - 5 pA
Ne – 1.9 nm; 0.1 - 2.5 pA
Accelerating Voltage
• 10 – 35 kV
Switching time between gases
~1 min
ETDetector
Electron Flood Gun
Sample
SE
Helium + Neon
Target Specs.
Higher sputter yield (30% greater than helium)
Shallower penetration depth
Higher SE yield compared to He - 3X faster resist exposure than He
Improved deposit quality – Metal deposit resistivity equivalent to Ga
Neon Beam Benefits
High resolution imaging using He combined with
High fidelity nanostructuring using Ne
59
9/20/2012 Page 60
Carl Zeiss NTS LLC , Bernhard Goetze
Cryogenic Cooling
Gas InletHigh Voltage
High Speed Camera
Phosphor Screen
Gas Field Ion Source
61
The Technology Behind It
Individual atoms are stripped away from the source until an atomic pyramid is created with just three atoms at the very end of the source tip – a configuration called the trimer.
Once the trimer is formed, the tip is maintained under high vacuum and cryogenic temperatures with helium or neon gas flowing over it.
The helium or neon atoms are attracted to the energized tip where they are ionized.
With ionization happening in the vicinity of a single atom, the resulting ion beam appears to be emanating from a region that is less than an angstrom in size.
FIM tip created via chemical etching
ALIS tip formed with additional reshaping
3 atom shelf called the “trimer” created through field evaporation
Single atom selected to form the final probe
Results in a sub-angstrom virtual source with high brightness (4x109 A/(cm2 sr)) and low energy spread (<1eV)
The Atomic Level Ion Source
62
ORION NanoFab– The Column
9/20/2012
Bulk Milling with Ga
Multi-ion Beam Machining in ORION NanoFab
Intermediate Milling with NeFinal Milling with He
Sample: Gold film on Glass substrate
Ga Milling
He Milling
Ne Milling
64
Nanofabrication
Why He ions for Imaging?
HeiM on Graphene
Summary
•
•
•
Orion NanoFAab technology•
Conclusions•
Introduction•
More Applications•
The ORION NanoFab Platform
• Configurable architecture to address specific imaging and nanofabrication applications.
• High Resolution Imaging on insulating samples – ideal for life science and polymer imaging applications.
• 3D Nanofabrication of sub-10nm structures.
• Precise Machining with He/Ne beams and Rapid Prototyping with Ga beam – only platform offering unique combination of three different ion beams.
Sample
Helium + Neon
Ga XRE
Stereocilia
9/20/2012 67
Carl Zeiss NTS LLC , Bernhard Goetze
200 nm
HIM: Unsurpassed Resolution 0,24nm
Carbon Nanotubes (Provided by Prof. Brendan Griffin Univ. W. Australia)
CNT
HIM: Low Damaging Effect
MEMS
HIM: High Depth of Field
Collagene
HIM: Effective Charge Compensation
(Provided by Prof. Brendan Griffin Univ. W. Australia)
CNTHIM: Surface Details
9/20/2012 72Carl Zeiss NTS LLC , Bernhard Goetze
Collecting Duct
HIM: High Resolution and Elevated Surface Details
500nm
Catalyst: Pd on ZnO nanowires
73
HIM: High Depth of Field
Bacteria
9/20/2012 74Carl Zeiss NTS LLC , Bernhard Goetze
200 nm
HIM: Minimal Sample Preparation
HIM: Nanofabricaation with Ga ions
75
TEM lamella S/C
200nm
76
Al bump su Silicio
HIM: Nanofabricaation with Neon ions
100nm
~4nm gap
TEM Image
77
Plasmonic Devices
HIM: Nanofabricaation with He ions
Bulk Milling with Ga
Multi-ion Beam Machining in ORION NanoFab
Intermediate Milling with NeFinal Milling with He
Sample: Gold film on Glass substrate
Ga Milling
He Milling
Ne Milling
78
HIM: Nanofabricaation with Multiple Beam
Plasmonic Devices
79