Atomic Layer Deposition:

Atomic Layer Deposition:
Geschichte, Grundlagen und Innovative Anwendungen
Atomic Layer Deposition
Sequential, self-limiting gas-solid surface reactions.
Knez, Nielsch and Niinistö, Adv. Mater. 19, 3425 (2007)
Video by S. Martens (IAP)
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CVD vs. ALD
CVD
When the precursor molecule
reaches the substrate, it
decomposes immediately and it
is coated rapidly by the
following molecules.
ALD
Controlled, slow, layer-bylayer deposition from two
species
of
precursor
molecules.
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CVD vs. ALD
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Diffusion controls the growth rate
Deposition rates > 0,1 µm / min
Roughness > 1 µm
Temperature T = 400-800°C
Mostly crystalline Structures
Suitable only for planar substrates
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Chemistry controls the growth rate
Deposition rate < 0,1 nm / min
Roughness < 1 nm
Temperature T 100-300°C
Amorphous Structure
Suitable for complex Geometries
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ALD Window
The Periodic Table of Elements
Miikkulainen et al., J. Appl. Phys. 113, 021301 (2013)
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History of ALD
• Beginning of 90ths: Common name was atomic layer epitaxy (ALE).
• Pioneer of ALD: Dr. Tuomo Suntola – Development of ZnS process for
in the early 70th‘s.
• First (industrial) application: Electroluminescent displays used at the
Helsinki airport until 1998.
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History of ALD II
• Parallel to Finish activities, Aleskovski and Kol’tsov worked on
“molecular layering reactions” in the former Soviet Union.
• Open online-project to unveil the history and roots of ALD:
http://aldpulse.com/node/189
Conference: 14th Int. Conf. on Atomic Layer Deposition, At Kyoto, Japan
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The Global Push of ALD: high-k Dielectrics
• Miniaturization of electronic devices
• Isolation layer of gate electrodes in
MOSFETs (field-effect transistors) has
reached a few nm
• SiO2 Layer can not be controlled
sufficiently
• Controlled method for the deposition
of thicker oxide layers with a high
dielectric constant
Prototype of a Commercial Reactor
Cambridge NanoTech Inc.
Investment Costs
ALD Reactor Development
2005
2010
Development
of Price
Future in our Lab
Development
of Price
2010
Future
A Look in Our ALD Lab
Material
Precursor
T/ C
Al2O3
TMA, H2O
RT – 300
SiO2
APTES, H2O, O3
120 – 300
ZnO
Diethyl Zink, H2O
80 – 250
MgO
Mg(CpEt)2, H2O
125 – 300
NiO
Nickelocen, O3
200 – 300
CoO
Cobaltocen, O3
200 – 300
Fe2O3
Ferrocen, O3
200 – 300
Ni
Ni(dmamb)2, NH3
250
Co
Co(iPr-AMD)2, NH3
250
Y2O3
Y(MeCp)3, H2O
200
ZrO2
TEMAZr, H2O
200
TiO2
Ti Isopropoxid, H2O
RT –300
CoxFe3-xO4
Cobaltocen, Ferrocen, O3
250 – 300
NixFe3-xO4
Nickelocen, Ferrocen, O3
200 – 300
NixCo3-xO4
Nickelocen, Cobaltocen, O3
250 – 300
Sb
(Et3Si)3Sb, SbCl3
120
SbTe2
(Et3Si)2Te, SbCl3
85 – 120
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Different Reactor for Different Application
Batch reactor
Plasma-ALD
Spatial ALD
Direct-write
Roll-to-roll
Time domain
Spatial domain
Kessels and Putkonen, MRS Bulletin 36, 907 (2011)
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Drum Reactor for Nanoparticle Coating
Powder + ALD Coating
Spark Plasma Sintering
Nanostructured Bulk
PhD thesis Sebastian Zastrow
Master thesis Julia Gemmer
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ALD on Thermoelectric Nanoparticles
Electron microscopy reveals conformal coating of particles
1 µm
200 nm
Al2O3 thickness
influences
TE bulk properties
PhD thesis Sebastian Zastrow
Master thesis Julia Gemmer
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Supercycle ALD for Ternary Materials
Alternating ALD cycles
can lead to ternary
materials.
A few examples:
NixFeyOz
CoxFeyOz
SrxTiyOz
GexSbyTez
ITO, ZTO
YSZ
High-k materials
precursor 1
precursor 2
precursor 3
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Ternary Materials: Tailor-Made Properties
nickel/ cobalt ferrite
ZnSnOx
Adjusting energy band levels
Chong, Nielsch et al., Chem. Mater. 22, 6506 (2010)
Kapilashrami et al., Phys. Chem. Chem.Phys. 14,10154 (2012)
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An Example: SnZnOx in CIGS Solar Cells
ALD is used to engineer
the electrical junction
properties of the solar cell
diode.
Solar cell efficiency depends on
stoichiometry in buffer layer.
Lindahl et al., Prog. Photovoltaics Res. Appl. 21, 1588 (2013)
Hultqvistet al., Prog. Photovoltaics Res. Appl. 20, 883 (2012)
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ALD of Nanoparticles
Supercyclic ALD of Ru(DER), Pt(MeCp)Me3 and O2
leads to Ru-Pt-alloy nanoparticles…
Nucleation delay by film growth
due to different surface energies
can be used to deposit nanoparticles.
…revealing higher thermal (catalytic) conversion of
methanol than a mixture of pure metallic particles.
Christensen et al., Nano Lett. 10, 3047 (2010)
Kim et al., Thin Solid Films 517, 2563 (2009)
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Field-Effect Devices
Nanochannels - Ionic FET
MOS/FIN-FET
250 nm
250 nm
100 nm
250 nm
Nam et al., Nano Lett. 10, 3324 (2010)
Johnson et al., Mater. Today 17, 236 (2014)
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Ferrofluidic Suspensions
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High-Aspect Ratio Templates
ALD
Tailor-Made Nanotubes:
• Material
• Diameter
• Length
• Wall Thickness
PhD thesis Robert Zierold
Zierold, Nielsch et al., Adv. Funct. Mater. 21, 226 (2011)
Zierold, Nielsch et al., Phys. Status Solidi B 247, 2412 (2010)
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Nanotube Ferrofluids
PhD thesis Robert Zierold
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Zierold, Nielsch et al., Adv. Funct. Mater. 21, 226 (2011)
Zierold, Nielsch et al., Phys. Status Solidi B 247, 2412 (2010)
Magnetoviscosity
Same MVE response in a ten times
more diluted liquid nanotube suspension
compared to a commercial ferrofluid,
BUT higher sensitivity at lower magnetic
fields.
PhD thesis Robert Zierold
Zierold, Nielsch et al., Adv. Funct. Mater. 21, 226 (2011)
Zierold, Nielsch et al., Phys. Status Solidi B 247, 2412 (2010)
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Hybride Ferrofluids
+
Hybrid suspensions consisting of nanotubes and commercial
spherical
nanoparticles
reveal
drastically
increased
magnetoviscous effects and might pave a way towards
industrial applications.
PhD thesis Robert Zierold
Zierold, Nielsch et al., in preparation (2014)
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Electrocatalytic Water Splitting
Synthesis Scheme
Iron oxide is a low-cost, biocompatible
material which can act as catalyst.
ALD allows for Synthesis of
High Surface Area Catalyst
flat substrate
Gemmer et al., J. Catalysis 290, 220 (2012)
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Photonic Crystals for TBC
(Thermal Barrier Coating)
Broadband Reflector im NIR
Temperature
Decrease
by 13 °C at a Working
Temperature of >1000 °C
Life-time doubling
d2 = 756 nm
d1 = 608 nm
Detailed Information at Poster (Dr. Robert Zierold)
Kelly, M et al., Int. J. Appl. Ceram. Technol. 3, 81 (2006)
Zierold, Nielsch et al., J. Opt. Soc. Am. B 29, 450 (2012)
Zierold, Nielsch et al., J. Am. Ceram. Soc. 95, 2226 (2012)
Zierold, Nielsch et al., Optical Materials Express 3, 1007 (2013)
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Introduction: Topological Insulator
Cartoon: Dirac dispersing
surface states lying in the
bulk band gap
Energy and momentum dependence of the local density
of states on the [111] surface. Here, the warmer colours
represent higher local density of states.
Sb2Te3
Bi2Se3
Bi2Te3
H. Zhang et al., Nature Physics 5, 438 (2009).
ALD of Thermoelectric Materials
SbCl3 + (Et3Si)2Te
Sb2Te3
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PhD thesis Sebastian Zastrow
Zastrow, Nielsch et al., Semicond. Sci. Technol. 28, 035010 (2013)
Thermoelectric Properties of ALD Thin Films
Thickness Dependence
Decreasing film thickness
Seebeck Coefficient decreases continuously
Conductivity behaves non-monotonically.
PhD thesis Sebastian Zastrow
Zastrow, Nielsch et al., in preparation (2014)
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Topological Surface States
Indications for TI surface states
PhD thesis Sebastian Zastrow
Zastrow, Nielsch et al., in preparation (2014)
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Thickness Dependence – 2 regimes
Bulk Carrier
Surface
Bulk
Surface
Thickness dependence:
t < 72: sigma ~ 1/t
Thickness dependence:
t > 72 nm: sigma ~ t
TMR Devices
ALD is ideally suited to prepare ultra-thin, pin-hole free films.
A prerequisite for tunnel barriers:
Results are comparable to (first)
sputtered film.
New emerging field (only few publications): Al2O3, MgO, HfO2
Liu et al., Appl. Phys. Lett. 102, 202401 (2013)
Mantovan et al., J. Phys. D: Appl. Phys. 47, 102002 (2014)
Zierold, Nielsch et al., submitted to Appl. Phys. Lett. (2014)
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Water Diffusion Barrier for Organic Devices
80°C, 80 % humidity
Water Vapor Transport Ratio at ambient conditions: 8E-7 g/(m2 d)
close to industrial requirements
Groner et al., Appl. Phys. Lett. 88, 051907 (2006)
Meyer et al., Adv. Mater. 21, 1845 (2009)
Meyer et al., Appl. Phys. Lett. 96, 243308 (2010)
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ALD (Extreme) on Biological Templates I
Filling the inner channel of a tobacco mosaic virus.
Length: 300 nm outer Ø : 18 nm inner Ø : 4 nm
Knez et al., Nano Lett. 6, 1172 (2006).
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ALD on Biological Templates II
Coating/ Infiltration of Spider Silk
ALD can be used to significantly
enhance the strain (stress)
curves.
2009 Apr 24;324(5926):488-92
Lee et al., Science, 324, 5926 (2009)
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ALD for Improving Battery Performance
ALD of ultra-thin Al2O3-layers on LiCoO2 electrodes
Improved retention of capacity vs. charge/discharge cycle number.
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Suppress structural instabilities related to lithium insertion and desertion.
Act as solid electrolyte and prevent direct contact between cathode surface and electrolyte.
Jung et al., J. Electrochem. Soc., 157, A75 (2010)
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Pt ALD for Solid-Oxide Fuel Cells
Pt can act as catalyst to allow for reduction of working
temperature by retaining the fuel-cell performance.
Largest boundary density improves SOFC
performance by about 90 %.
NP growth
Coalescence of NPs
optimal
closed Pt-film
400 °C
Chao et al., Adv. Energy Mater., 2, 651 (2012)
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YSZ ALD for Solid-Oxide Fuel Cells
Yttria-Stabilized Zirconia deposited by supercyclic ALD acts a
electrolyte in SOFC.
Nanocrystalline ALD membranes show 4 orders of
magnitude enhanced exchange-current density compared
to reference (bulk >100 µm) membrane.
Chim et al., Chem. Mater., 19, 3850 (2007)
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Cathode Passivation in SOFC by ALD
Cathode material La0.6Sr0.4CoO3-δ (LSCo) coated with ZrO2
Overcoated samples show compared to pure SOFC‘s cathode:
• time-dependent stable (small) polarization area-specific R
• 18times reduced degradation
Gong et al., Nano Lett., 13, 4340 (2013)
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Spatial ALD for Solar Cell Passivation
A Proof-Of-Principles
150 mm wafer ( 30 mm wide track)
Literature value
(for „standard“ ALD)
• Deposition rate: 1.2 nm/s.
• Lifetimes of 5 ms for minority carrier
densities of 1015 cm-3 (corresponding
to surface recombination velocity <2
cm/s). Comparable to state-of-the-art.
Poodt et al., Adv. Mater., 22, 3564 (2010)
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Nanopatterning by ALD
1
2
3
Mackus et al., Nanoscale DOI:10.1039/c4nr01954g (2014)
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Nanopatterning by ALD
1
2
3
Mackus et al., Nanoscale DOI:10.1039/c4nr01954g (2014)
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Nanopatterning by ALD
1
2
3
Mackus et al., Nanoscale DOI:10.1039/c4nr01954g (2014)
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Selective ALD on OTMS-Functionalized Al2O3 Nanopores
3D Metal/Oxid Nanostructures based on ALD
TiO2 coated
Tobacco Mosaic Virus
Core-Shell
Magnetic Nanowires
Ø54 nm Ni core
25 nm SiO2
Ø54 nm Ni core
M. Knez et al., Nano Lett. 6,
1172 (2006).
1825nm
nm Fe
SiO32O4
nm Fe3O4
518nm
SiO2
5 nm SiO2
Ni und Co Nanotubes
M. Daub et al, J. Appl. Phys.
101, 09J111 (2007).
C.Y. Chong et al,
Adv. Mater. 22, 3170 (2012)
Collaboration with
Prof. M. Eich (TU-Harburg)
Danksagung - Acknowledgements
Gruppe Nielsch – IAP, Universität Hamburg
We gratefully acknowledge financial support via the German Priority
Programs DFG-SPP 1386 nanoTE and DFG-SPP 1538 SpinCat.

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