ALD for Industry 2019: Slides of invited tutorial by Prof. Riikka Puurunen

Puurunen, Tutorial, ALD for Industry, Berlin, 19.3.2019
Invited tutorial
ALD Technology – Introduction,
History & Principles
Prof. Riikka Puurunen, Aalto University School of Chemical Engineering
ALD for Industry, Berlin, March 19-20, 2019

Atomic layer deposition (ALD)
ALD cycle
Reactant A
Reactant B
By-product
Substrate
before ALD
Step 2 /4
purge
Step 4 /4
purge
Step 1 /4
Reactant A
Step 3 /4
Reactant B
Reactant A
Reactant B
By-product
(scheme: Puurunen)
George, Chem. Rev. 110 (2010) 111–131.
DOI: 10.1021/cr900056b
 Time 

20.3.2019
3
Associate professor,
Catalysis Sci. & Tech.,
Aalto University
1999-2002,
Catalysis,
D. Sc. (Tech.)
HUT
1998,
M.Sc.,
HUT
2003-2004, postdoc,
microelectronics, IMEC, Belgium
2004-2017, MEMS
(Senior) researcher, project
manager, VTT, Finland
2017 
(ALD) career overview,
Riikka Puurunen
2013 , Virtual
Project on the
History of ALD
publications: 57, H-index 24
2005, review in
J. App. Phys.,
>1300 citations
2015 , ALD film
conformality test
concept
?
times cited: 3502

Outline
• (Very brief introduction of topic and speaker)
1. On the history of ALD: who, when, why, what?
2. Surface chemistry of ALD – Terminology, mechanisms,
conformality analysis
3. Surface chemistry of ALD – Some progress notes
4. Where ALD used?
5. Conclusion
• (Additional material)
#ALDep
Panopto

On the history of ALD:
Who, when, why, what?

ALD discovered independently twice
Atomic layer epitaxy (ALE)
1974 
Molecular Layering (ML)
? ~1965 
Dr. Tuomo S. Suntola
Espoo, Finland
Photo:RiikkaPuurunen,27.7.2017
Prof. Valentin B. Aleskovskii
Prof. Stanislav I. Koltsov
St. Petersburg, USSR / Russia
https://en.wikipedia.org/wiki/Tuomo_Suntola, https://en.wikipedia.org/wiki/Valentin_Aleskovsky

TechnologyAcademyFinland2019

Essay: Puurunen, Chem. Vap. Deposition 20 (2014) 332-344. https://doi.org/10.1002/cvde.201402012
1974
Electroluminescent displays

1987 Suntola:
Microchemistry
F-120
Small research reactors, solar panels (CdTe),
catalysts (powder ALD),   microelectronics
MRS 1994
Review: Parsons et al. J. Vac. Sci. Technol. A 31 (2013) 050818. https://doi.org/10.1116/1.4816548

Prof.MarkkuLeskelä’sretirementlecture,6.3.2019
UniversityofHelsinki,
PhotobyRiikkaPuurunen
• Helsinki University of Technology (Espoo)  Prof. Niinistö, Leskelä
• (Part of) research moved to Univ. of Helsinki (Helsinki) with professorship of Leskelä
• Three-colour displays made by
filtering from ZnS:Mn yellow
(not new new chemistry)
• Colour development brought
significant expertise in ALD
process development
(Full) colour ALE-EL display?
?


Suntola, Mater. Sci. Reports 4 (1989) 261–312. https://doi.org/10.1016/S0920-2307(89)80006-4
1989
1. Finland
2. Japan
3. USA
4. …

Essays in Chem. Vap. Deposition
On Atomic Layer Epitaxy, by Puurunen On Molecular Layering, by Malygin et al.
Puurunen, Chem. Vap. Deposition 20 (2014) 332-344.
https://doi.org/10.1002/cvde.201402012
Malygin et al., Chem. Vap. Deposition 21 (2015) 216-240.
https://doi.org/10.1002/cvde.201502013
2015
2004, European SEMI Award at
the Munich Electronics Show
2004, In the winter garden of the St. Petersburg
State University … conference “Chemistry of highly
organized substances and fundamental scientific
basics of nanotechnology“
2014

(review article) V. B. Aleskovskii,
“ Chemistry and technology of
solids,” Zh. Prikl. Khim. 47, 2145
(1974) V. B. Aleskovskii [J. Appl.
Chem. USSR 47, 2207 (1974)].
1974

• (10.1149/08606.0003ecst, Ref. 32) V. B. Aleskovskii and S. I. Koltsov, “Some characteristics of molecular layering
reactions,” in Abstract of Scientific and Technical Conference of the Leningrad Technological Institute by Lensovet
(Goskhimizdat, Leningrad, 1965), pp. 67–67 (in Russian, English title translated in the VPHA. Original title in Russian:
“Некоторые закономерности реакций молекулярного наслаивания”).
• Discussed in Section III.B.1 in: Ahvenniemi et al. (62 authors), J. Vac. Sci. Technol. A 35 (2017) art.
010801; https://doi.org/10.1116/1.4971389. [Included as Ref. 51: V. B. Aleskovskii and S. I. Koltsov, “Some
characteristics of molecular layering reactions,” in Abstract of Scientific and Technical Conference of the Leningrad
Technological Institute by Lensovet (Goskhimizdat, Leningrad, 1965), pp. 67–67 (in Russian).]
1965
First written
record of
”Molecular
Layering” (?)

Applications of Molecular
Layering - ALD?
https://commons.wikimedia.org/wiki/File:Russian-Matroshka_no_bg.jpg
It’s like…

Visions of Aleskovskii, 1974
Entry #9 in https://doi.org/10.1116/1.4971389 (VPHA): ” The review reflects the vision of the
Aleskovskii group(s), reviewing advances made by 1974 and predicting what could be achieved by
molecular layering. Aleskovskii presents an early suggestion of surface-selective deposition: “if
necessary, part of its <i.e., support's> surface is shielded by flat (monolayer) or relief coating in the
form of specified pattern.” He also notices the possibility of using templates for growth “at the end
of the synthesis, the support is removed, if necessary, by chemical or mechanical methods.” He
notices the possibility of fine regulation of pore size in sorbents and concludes that ML works in
a similar manner on single crystals (e.g., silicon, germanium), porous materials (e.g., silica gel,
carbon), and fine powders (e.g., talc, kaolin, aerosil). He notices, using several examples, that four
to six “monolayers” (the name he used for ML cycles) are needed for the material to reach the
properties that the solid material would have. He describes the deposition of ternary materials
(TiO2 and POx combined as a mixed oxide) where the sequence of depositions in total of
four ALD cycles (14 possible combinations of cycles, all synthesized) influences the catalytic
activity of the system. Striking is Aleskovskii's comment on the potential applications of ML in the
down-scaling of semiconductor technology: “The route to further miniaturization of
microelectronic devices and to molecular electronics is evident.””
V. B. Aleskovskii, “ Chemistry and technology of solids,” Zh. Prikl. Khim. 47, 2145
(1974) [J. Appl. Chem. USSR 47, 2207 (1974)].
Ahvenniemi et al. (62 authors, alphabetical order), Review Article: Recommended reading list of early publications
on atomic layer deposition—Outcome of the “Virtual Project on the History of ALD”, J. Vac. Sci. Technol. A 35
(2017) art. 010801; https://doi.org/10.1116/1.4971389

Malygin et al., Chem. Vap. Deposition 21 (2015) 216-240. https://doi.org/10.1002/cvde.201502013
http://vph-ald.com/UploadedPublications/Malygin-ALD2016-25July.pdf
ALD reactor
cell with
in situ
ellipsometry
1975
Reactors, in-situ analysis, sorbents, catalysts,
coatings to lower sintering temperature, humidity
indicators, semiconductor-related tests,…
Thin film reactor 1977
Powder
processing
1987
Malygin: >600 papers,
>70 patent certificates,
… (ALD 2016 info)

(Abstract) This paper … presents a recommended reading list of early ALD publications,
created collectively by the VPHA participants through voting. The list contains 22 publications
from Finland, Japan, Soviet Union, United Kingdom, and United States. Up to now, a
balanced overview regarding the early history of ALD has been
missing; the current list is an attempt to remedy this deficiency.
J. Vac. Sci. Technol. A 35 (2017) art. 010801; https://doi.org/10.1116/1.4971389
2017, 62 authors

Time to write another review?
VPHA collaboration planned,
Open Science; more volunteers welcome
vph-ald.com

Surface chemistry of ALD –
Terminology, mechanisms,
conformality analysis

Definition of ALD – is there one?
” ALD can be defined as
a film deposition
technique that is based on
the sequential use of self-
terminating gas–solid
reactions”
Puurunen, 2005
ALD cycle
Reactant A
Reactant B
By-product
Substrate
before ALD
Step 2 /4
purge
Step 4 /4
purge
Step 1 /4
Reactant A
Step 3 /4
Reactant B
Reactant A
Reactant B
By-product
Puurunen, J. Appl. Phys. 97 (2005) 121301. DOI: 10.1063/1.1940727
Open Access: https://www.vtt.fi/inf/julkaisut/muut/2010/Puurunen.pdf

Self-terminating
 Saturating & irreversible
desorptionnon-saturation unsaturation
amount adsorbed saturates
amount adsorbed stays
NO:
pulse purge
Puurunen, J. Appl. Phys. 97 (2005) 121301. https://doi.org/10.1063/1.1940727 open access pdf
sequential use of self-terminating
gas–solid reactions

Gas-solid reactions
 Chemical adsorption
Physisorption
• non-specific
• minimal electronic interaction
• chemical nature of the adsorbate
not altered
• adsorption energy similar to the
energy of condensation
(exothermic)
• non-activated
• equilibrium is established
• multilayers may form
Chemisorption
• chemical specificity
• changes in electronic state
• reversible/irreversible
• chemisorption energy as for a chemical
reaction (exothermic/endothermic)
• often involves an activation energy
• for “large” activation energies (“activated
adsorption”), true equilibrium may be
achieved slowly
• monolayer adsorption
http://old.iupac.org/reports/2001/colloid_2001/manual_of_s_and_t/node16.html

ALD: (simplified) variant of CVD
Image: Pedersen, H. & Elliott, S.D. Theor Chem Acc 133 (2014) 1476. https://doi.org/10.1007/s00214-014-1476-7
x
in ALD: gas phase reactions excluded,
(ideally) irreversible reactions
CVD: continuous flow
ALD: separate pulsing
of reactant vapors
xadsorption
x

Growth per cycle (GPC)
• ALD is characterized by
a GPC, which depends
typically on:
• reactants
• temperature
• substrate
• In ALD, there is no
”growth rate” in the
sense as e.g. in CVD

>700 ALD reactant - co-reactant pairs
26
H2O
NH3
H2S
Non-metal co-reactants, “thermal” ALD
Energy-enhanced ALD
O2
N2
H2
Metal precursor type
Elements
Halides
Alkyls
Cyclopentadienyls
Alkoxides
b-diketonates
Alkylamides and
silylamides
Amidinates
InorganicMetal-organic
Organo-
metallic
Class
N
NM
N
M
O
M
O
O
M
M
M
M
Cl
M
etc
etc
Puurunen, Appl. Phys. 97 (2005) 121301. https://doi.org/10.1063/1.1940727
Miikkulainen, Leskelä, Ritala, Puurunen, J. Appl. Phys. 113 (2013) 021301. http://dx.doi.org/10.1063/1.4757907.
O3
…
Metal reactant type

Chemisorption
mechanisms
typical in ALD
Fig. 11, Puurunen, J. Appl.
Phys. 97 (2005) 121301.
https://doi.org/10.1063/1.19
40727 open access pdf
Dissociation
L
Reaction:
MLn + surface
L/M < n
L/M = n
L/M = n

Chemisorption mechanisms - 2
Barry, Teplyakov, Zaera, Acc. Chem. Res. 51 (2018) 800–809. DOI: 10.1021/acs.accounts.8b00012
(graphical summary; solution-related parts removed)
Note mechanistic
difference of
dissociation
compared with
J. Appl. Phys. 97
(2005) 121301.
https://doi.org/10.10
63/1.1940727
L
L

Monolayer – three different
Chemisorbed monolayer
Physisorbed monolayer
Monolayer of
ALD-grown material
GPC typically
<50% of a
monolayer

ALD window
Suntola, ”Atomic layer epitaxy” Mater. Sci. Rep. 4 (1989) 261-312.
DOI: 10.1016/S0920-2307(89)80006-4
Explanations (shortened)
L1: condensation to be prevented
L2: activation energy to exceed
H1: decomposition
H2: re-evaporation
GPC variations within an ALD window
Puurunen, J. Appl. Phys. 97 (2005) 121301.
https://doi.org/10.1063/1.1940727 open access pdf
For Suntola’s newer views, see:
http://aldhistory.blogspot.com/2019/03/mtp2018-suntola-photos-from-May23-2018.html, accessed 16.3.2019
#ALDepWindow

Conformality
Cremers, Puurunen,
Dendooven, Appl.
Phys. Rev. (2019) in
press, DOI:
10.1063/1.5060967
in atomic layer deposition: Current status
overview of analysis and modelling
To analyse: ”Infinite”
lateral high-aspect
ratio test structures
(LHAR)
In press
Not conformal Conformal

(Hole-)equivalent aspect ratio (EAR)
Cremers, Puurunen, Dendooven, Appl. Phys. Rev. 2019, DOI:10.1063/1.5060967
Ylilammi, Ylivaara, Puurunen, J. Appl. Phys. 123, 205301 (2018); DOI: 10.1063/1.5028178
50% pene-
tration depth
(PD50%)
0.5
In press

EAR
Cremers, Puurunen, Dendooven, Appl. Phys. Rev. 2019, DOI:10.1063/1.5060967
[Comparison before EAR: Mattinen et al., Langmuir 32 (2016) 10559–10569, doi:10.1021/acs.langmuir.6b03007]
In press
PD50%

Saturation profile
 ALD observable? Yanguas-Gil, 2017
Thickness(nm)
Unpublished data, PillarHall LHAR3
 Should the thickness be normalized?

Surface chemistry of ALD –
Some progress notes

Some surface chemistry questions
1. Which material is grown?
2. Is the growth self-terminating  is it ALD?
3. What is the temperature range where ALD growth occurs? ( ALD window?)
4. How much material is grown in an ALD cycle; what is the GPC?
5. Which gaseous byproducts form and when?
6. (Do byproducts re-adsorb on the surface?)
7. Which surface species are formed? How much of them?
8. Through which mechanisms does (reactive) adsorption take place?
What defines GPC?
9. How does the GPC vary within in the ALD window, and why?
10.Are there impurities in the film & (how) do they affect the film growth?
11.How fast are the surface reactions; kinetics of growth?
Can you think of more
questions?
https://www.atomiclimits.com/2019/02/12/atomic-layer-deposition-process-development-10-steps-to-
successfully-develop-optimize-and-characterize-ald-recipes/  recommended post on process development

Prototype ALD process:
trimethylaluminium/water  Al2O3
Status acknowledged/agreed e.g. in:
• Puurunen 2005, review on the TMA/water
process, DOI: 10.1063/1.1940727
• George 2010, DOI: 10.1021/cr900056b
• Miikkulainen et al. 2013, DOI:
10.1063/1.4757907
• Knapas & Ritala 2013, DOI:
10.1080/10408436.2012.693460
• Weckman & Laasonen 2018, DOI:
10.1039/C5CP01912E
• Van Bui et al. 2017, DOI:
10.1039/c6cc05568k
Van Bui, Grillo, Van Ommen, Chem. Commun. 53 (2017) 45. DOI: 10.1039/c6cc05568k
#TMAwater

ALD window: r.t. up to ~300°C (wide!)
38
300°C
327°C
350°C
250°C200°C150°C80°C
Puurunen et al., Phys. Chem. Chem. Phys. 3 (2001) 1093. http://dx.doi.org/10.1039/B007249O
Review: Puurunen, J. Appl. Phys. 97 (2005) 121301; https://doi.org/10.1063/1.1940727 & references therein
Surface saturates with reaction products
No saturation:
Reactant decomposes
AlMe3 reaction temperature (K) on alumina
Carbonatoms(nm-2)

GPC?
• GPC ~0.1 nm
• GPC ~30% of
monolayer
• GPC decreases
with temperature
Review: Puurunen, J. Appl. Phys. 97 (2005) 121301; https://doi.org/10.1063/1.1940727 & references therein

“Correlation between the growth-per-cycle and the
surface hydroxyl group concentration in the atomic layer
deposition of aluminum oxide from trimethylaluminum
and water”
Puurunen, Appl. Surf. Sci. 245
(2005) 6-10.
DOI:10.1016/j.apsusc.2004.10
.003
• ~All OH groups
react & release a
ligand (CH4)
• Reaction stops
because of steric
hindrance
L/M
Ligand
exchange
Dissociation/
association

Kinetics? Sticking probability?
Slope of the
leading edge of
saturation profile
related to reaction
kinetics
Knoops et al., J. Electrochem. Soc. 157 (2010) G241-G249. DOI: 10.1149/1.3491381
Cremers, Puurunen, Dendooven, Appl. Phys. Rev. (2019) in press, DOI: 10.1063/1.5060967

Kinetics? Sticking probability?
In press

Langmuir adsorption model in
sticking probability derivation
20.3.2019
43
https://en.wikipedia.org/wiki/Langmuir_adsorption_
model#/media/File:Langmuir_Adsorption_Model.jpg
Ylilammi, Ylivaara, Puurunen, J. Appl. Phys. 123, 205301 (2018); DOI: 10.1063/1.5028178
https://en.wikipedia.org/wiki/Langmuir_adsorption_model, accessed 13.9.2018
• Flat surface & isothermal conditions
• Surface sites are equal
• Adsorbed species do not interact
• Adsorption & desorption are elementary processes
Association

Real ALD is more complex
20.3.201944
Langmuir adsorption
reality
Association
Ligand exchange
Dissociation
Association
No adsorbate-adsorbate interactions
Adsorbate-adsorbate
interactions

Where ALD used?

VPHA poster submission ALD 2019
On the list collection of doctoral theses on ALD worldwide
http://aldhistory.blogspot.com/2019/02/vpha-communication-ald2019-abstract-submitted.html
https://twitter.com/rlpuu/status/1096385902971113472
• Japan? Australia?
• Germany (more)?
• …?

Conclusion

Conclusion
• ALD discovered twice; history (still) not in general well
presented in books / review articles
• 1974, Initially industrial; electroluminescent displays
• 1960s, Academic; wide scope
• Basics of ALD ~well understood; views & terminology evolving
• Recent progress in conformality measurement & analysis
• Opportunities to create fundamental understanding on ALD

Additional materials and links
• JAP 2005 review as teaching material & Do not mix up …
• Some interview links
• Reviews on surface chemistry of ALD
• ALD-related blogs
• About this tutorial presentation and the author
• Links to Panopto lecture capture
& Catalysis Professor’s Open blog

JAP 2005 review as teaching
material & Do not mix up …

The 2005 review by Puurunen
as teaching material
J. Appl. Phys. 97 (2005) 121301. DOI: 10.1063/1.1940727
• Times cited: 1327 (as of 8.11.2018, WoS)
• Section III written to explain the surface chemistry concepts
• Section V written to discuss problematic assumptions
• Review used for teaching ALD in several groups

Do not mix up: Molecular Layering and
Molecular Layer Deposition
• Molecular Layering: old Russian name for ALD
• Molecular Layer Deposition: variant of ALD where the reactants
are organic compounds instead of metal compunds

Do not mix up: Growth rate (e.g.
nm/cyc) & Growth rate (e.g. nm/min)
• Growth rate (nm/cyc) in ALD publications: same as GPC (nm)
• Growth rate (nm/min) in CVD publications: kinetic quantity

Some interview links

Where ALD?
Aalto University Magazine October 2018,
https://issuu.com/aaltouniversity/docs/aum_23_en_pdf-150dpi/24

Interviews of Suntola
https://twitter.com/icallan/status/1087754240871809024
http://peoplebehindthescience.libsyn.com/461-atomic-
layer-deposition-developer-fundamental-physicist-and-
scientific-philosopher-dr-tuomo-suntola

Interviews of Suntola – in Finnish
• https://twitter.com/rlpuu/status/11
02506280973942784
• https://areena.yle.fi/1-4452599
Tiedeykkönen Millennium-palkinto 2018: Tuomo
Suntolan nerokas ALD mahdollisti nykyiset
mikroprosessorit

Reviews on surface chemistry of
ALD

Reviews on surface chemistry of ALD
From: http://vph-ald.com/VPHAopenfiles.html ( list of ~200 reviews)
Suntola, Appl. Surf. Sci. 100/101 (1996) 391–398. http://doi.org/10.1016/0169-4332(96)00306-6
• Surface chemistry of materials deposition at atomic layer level
George et al., J. Phys. Chem. 100 (1996) 13121–13131. http://doi.org/10.1016/0169-4332(96)00306-6
• Surface chemistry for atomic layer growth
Puurunen, J. Appl. Phys. 97 (2005) 121301 (Appl. Phys. Rev.). https://doi.org/10.1063/1.1940727
• Surface chemistry of atomic layer deposition: a case study for the trimethylaluminum/water process
Zaera, J. Mater. Chem. 18 (2008) 3521–3526. http://dx.doi.org/10.1039/B803832E
• The surface chemistry of thin film atomic layer deposition (ALD) processes for electronic device manufacturing
Zaera, J. Phys. Chem. Lett. 3 (2012) 1301–1309. http://doi.org/10.1021/jz300125f
• The surface chemistry of atomic layer depositions of solid thin films
Probably there are more… e.g. Knapas & Ritala, Crit. Rev. Solid State Mater. Sci. 38 (2013) 167-202.
http://doi.org/10.1080/10408436.2012.693460 In Situ Studies on Reaction Mechanisms in Atomic Layer Deposition

ALD-related blogs

BALD Engineering Blog
http://www.blog.baldengineering.com/, accessed 16.3.2019
By Dr. Jonas Sundqvist

Atomic Limits Blog By Prof. Erwin Kessels and coworkers
https://www.atomiclimits.com/, accessed 16.3.2019
@atomiclimits

ALD History Blog
http://aldhistory.blogspot.com/, accessed 16.3.2019
By Prof.
Riikka Puurunen
@aldhistoryblog

About this tutorial presentation
and the author

Abstract, Prof Puurunen Keynote: ALD Technology – Introduction, History & Principles
ALD for Industry, Berlin, 19.-20.3.2019
This tutorial keynote will introduce atomic layer deposition (ALD) – a variant of chemical vapor
deposition - and fundamental principles and concepts related it from a generic viewpoint
applicable to any ALD process and reactor. The early history and current usage of ALD are
briefly overviewed: who made the first experiments, when, and why? How has the view on the
history of ALD evolved? Where is ALD now used, by whom, and why? ALD relies on repeated
chemical adsorption steps from gas phase to surface. The status of understanding the
adsorption steps of ALD films will be presented and discussed using mainly the archetype
trimethylaluminium-water ALD process as example and 3D conformality modelling as
additional vehicle. Plenty of links to further sources of information will be included in this
keynote presentation.

Description: Riikka Puurunen, Associate professor,
Catalysis Science and Technology, Aalto University
School of Chemical Engineering
Prof. Riikka Puurunen has worked with ALD since 1998 at different
locations (Microchemistry, HUT, IMEC, VTT, Aalto Univ) and with various
applications (catalysis, microelectronics and MEMS). Prof. Puurunen has
written several high-impact review articles, which have among other things
contributed to the acceptance of the trimethylaluminium-water process as
“model” or “archetype” ALD process; that a “periodic table of ALD materials”
has been created; and that the view on the history of ALD has been
renewed with another independent discovery. Prof. Puurunen has also
envisioned and realized new types of lateral microscopic conformality test
structures that enable exploration of ALD fundamentals new ways.

Tutorial programme 19.3.2019

aalto.fi
Panopto lecture capture:
https://aalto.cloud.panopto.eu/Panopto/Pages/Viewer.aspx?id=e05d5cde-
6e6c-4893-807d-aa150110c0e3
Related blog post in Catalysis Professor’s Open:
https://blogs.aalto.fi/catprofopen/2019/03/19/prof-puurunen-invited-tutorial-
at-ald-for-industry-berlin/

ALD for Industry 2019: Slides of invited tutorial by Prof. Riikka Puurunen

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ALD for Industry 2019: Slides of invited tutorial by Prof. Riikka Puurunen