Abstract of the presentation: Atomic layer deposition (ALD) is a thin film growth method generally applicable for the growth of conformal, highquality inorganic material layers down to the nanometer thickness range. ALD is indifferent to the morphology of the underlying substrate and covers even most complex 3-D shapes with a uniform film; as a consequence, ALD is used in an ever-increasing field of applications from catalysts to photovoltaics to microelectronics and beyond. ALD belongs to the general class of chemical vapour deposition (CVD) techniques. The speciality of ALD is the use of repeated self-terminating (saturating, irreversible) gassolid reactions of at least two reactants for the film growth; ALD is therefore non-continuous in nature, as opposed to the continuous CVD processes. In this presentation, I will discuss some challenges related to understanding the surface chemistry of ALD. The commonly-used trimethylaluminium-water ALD process to deposit Al2O3 is used as case example, as it is often presented as model case for ALD. I will also discuss the characteristics of ALD film conformality, as detected by using microscopic lateral high-aspect-ratio structures ("VTT μLHAR") [J. Vac. Sci. Technol. A 33, 010601 (2015)]. Here, the gap height is in the range of 100 nm's and the aspect ratio (AR) can be extremely challenging, e.g. up to 25 000:1. Finally, I will briefly introduce the on-going international volunteer-based Virtual Project on the History of ALD (http://vph-ald.com), where new participants are still welcome. Acknowledgement: The author thanks Finnish Centre of Excellence in Atomic Layer Deposition for funding.

1. VTT TECHNICAL RESEARCH CENTRE OF FINLAND LTD
Surface chemistry of ALD:
mechanisms and
conformality
98th Canadian Chemistry Conference
Surface Chemistry for Thin Film Deposition Session
Riikka L. Puurunen
VTT Technical Reseach Centre of Finland, Ltd.

2. 2R. L. Puurunen, Can. Chem. Conf., Ottawa, June 14, 2014
Outline
 Introduction to ALD
1. Me3Al/H2O  Al2O3:
Surface chemistry of the ALD model system
2. Thin film conformality analysis
3. History of ALD

3. 3R. L. Puurunen, Can. Chem. Conf., Ottawa, June 14, 2014
ALD: based on repeated self-terminating gas-solid
reactions (chemisorption)
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
ALD cycles
Mass
* Type of non-
continuous CVD
process

4. 4R. L. Puurunen, Can. Chem. Conf., Ottawa, June 14, 2014
Self-terminating gas-solid reactions in ALD:
saturating, irreversible
desorptionnon-saturation unsaturation
amount adsorbed saturates
amount adsorbed stays
NO:
pulse purge
Source: Puurunen (review), J. Appl. Phys. 97 (2005) 121301.

5. 5R. L. Puurunen, Can. Chem. Conf., Ottawa, June 14, 2014
ALD research status overview
Current version, ”2nd edition” (2010): Miikkulainen, Leskelä, Ritala, Puurunen (review), J. Appl. Phys. 113 (2013) 021301.
”1st edition” (2004): Puurunen (review), J. Appl. Phys. 97 (2005) 121301.
5

6. 6R. L. Puurunen, Can. Chem. Conf., Ottawa, June 14, 2014
Various types reactants (precursors) used
Source and further details: Puurunen, J. Appl. Phys. 97
(2005) 121301
Update: Miikkulainen, Leskelä, Ritala, Puurunen, J. Appl.
Phys. 113, (2013) 021301
H2O NH3
H2S
O3 N2
H2
”Normal” ALD
Energy-enhanced ALD (PEALD)
O2
Metal Non-metal
Inorganic compounds
Organometallic compounds
Metal-organic compounds

7. 7R. L. Puurunen, Can. Chem. Conf., Ottawa, June 14, 2014
1
Surface chemistry

8. 8R. L. Puurunen, Can. Chem. Conf., Ottawa, June 14, 2014
From: Puurunen, EuroCVD 2007 (in SlideShare)

9. 9R. L. Puurunen, Can. Chem. Conf., Ottawa, June 14, 2014
Me3Al/H2O – has evolved to The Model System
 Puurunen, 2005, J. Appl. Phys.
Me3Al/H2O surface chemistry critically reviewed & discussed
 George, 2010, Chem. Rev.
” The ALD of Al2O3 has developed as a model ALD system.
An earlier extensive review by Puurunen … [Puurunen2005]”
 Knapas & Ritala, 2013, Crit. Rev. Solid State Mater. Sci.
”The AlMe3 (TMA) – H2O process … the most studied ALD
system, and has also been adopted as a model system for
ALD [George2010].”
 Weckman & Laasonen, 2015, Phys. Chem. Chem. Phys.
” … the TMA/H2O system is considered as a model process for
ALD [George2010, Puurunen2005]”
859
930
(16)
Cited
WoS
12.6.2015
(0)

10. 10R. L. Puurunen, Can. Chem. Conf., Ottawa, June 14, 2014
 Puurunen, 2005, J. Appl. Phys.
Me3Al/H2O surface chemistry critically reviewed & discussed
 George, 2010: Chem. Rev.
” The ALD of Al2O3 has developed as a model ALD system.
An earlier extensive review by Puurunen …
[Puurunen2005]”
 Knapas & Ritala, 2013, Crit. Rev. Solid State Mater. Sci.
”The AlMe3 (TMA) – H2O process … the most studied ALD
system, and has also been adopted as a model system for
ALD [George2010].”
 Weckman & Laasonen, 2015, Phys. Chem. Chem. Phys.
” … the TMA/H2O system is considered as a model process
for ALD [George2010, Puurunen2005]”
Me3Al/H2O – The Model System
Let us treat the Me3Al/H2O process
with the critical eye
that the model system deserves

11. 11R. L. Puurunen, Can. Chem. Conf., Ottawa, June 14, 2014
Some fundamental questions related to ALD
 How does the GPC vary with temperature?
 What is the ALD window of a given process?
 What defines the Growth Per Cycle (GPC)?
  What is the limiting factor that causes saturation?
 Which surface reaction mechanisms take place?
 How fast are they?
Postulate: different works
explain the variation in GPC
in significantly different ways

12. 12R. L. Puurunen, Can. Chem. Conf., Ottawa, June 14, 2014
From: Puurunen, EuroCVD 2007 (in SlideShare)

13. 13R. L. Puurunen, Can. Chem. Conf., Ottawa, June 14, 2014
[Puurunen2005]
Fitting reference: Puurunen,
Appl. Surf. Sci. 245 (2005) 6-10
 Quantitative explanation of GPC
vs temperature via loss of [OH]
and ~constant [Me]
From: Puurunen, EuroCVD 2007 (in SlideShare)

14. 14R. L. Puurunen, Can. Chem. Conf., Ottawa, June 14, 2014
[Puurunen2005] Data behind the fitted equation
+ more data for [Me]
 Puurunen et al., J. Phys. Chem. B 104 (2000) 6599
 Puurunen et al., Phys. Chem. Chem. Phys., 3 (2001) 1093
From: Puurunen, EuroCVD 2007 (in SlideShare)
[Me]

15. 15R. L. Puurunen, Can. Chem. Conf., Ottawa, June 14, 2014
[Puurunen2005]
Field: Authors Record Count
KESSELS WMM 7
ADOMAITIS RA 4
POTTS SE 4
PUURUNEN RL 4
DINGEMANS G 2
DWIVEDI V 2
HARLIN A 2
KENTTA E 2
KIM J 2
KREUTZER MT 2
ROOZEBOOM F 2
SALO E 2
TRAVIS CD 2
VAHA-NISSI M 2
VAN HEMMEN JL 2
VAN OMMEN JR 2
WALLACE RM 2
Cited, 12.6.2015,
WoS: 36 times
From: Puurunen, EuroCVD 2007 (in SlideShare)

16. 16R. L. Puurunen, Can. Chem. Conf., Ottawa, June 14, 2014
[George2010]
”
”

17. 17R. L. Puurunen, Can. Chem. Conf., Ottawa, June 14, 2014
Data behind the conclusion: annealing experiment
300C100C
[Me]
[George2010]
Room-temperature exposure!
Qualitative description of GPC
vs temperature via loss of [OH]
and loss of [Me]

18. 18R. L. Puurunen, Can. Chem. Conf., Ottawa, June 14, 2014
[Knapas2013]
• No explanation for
temperature trends of GPC
• n/z value considered as
mechanism, weak trend
with temperature (if any)
• discussion on H2O dose
”
”

19. 19R. L. Puurunen, Can. Chem. Conf., Ottawa, June 14, 2014
Data behind, [Me]: QCM and QMS studies ref. 108
Ref 108
 Water not saturated (?)
 Was Me3Al saturated?
[Me]
[Knapas2013]

20. 20R. L. Puurunen, Can. Chem. Conf., Ottawa, June 14, 2014
Conclusion, The Model System
Source Puurunen, 2005 George, 2010 Knapas & Ritala,
2013
Explaination of
less-than-
monolayer GPC &
temp. trend
Quantitative Qualitative -
Description of
GPC change with
temperature
Decreases with
* decreasing [OH],
* [Me] ~constant
Decreases with
* decreasing [OH],
* decreasing [Me]
(* n/z about
constant at 1.5)
Background data,
Change of
surface [Me] vs
temperature
[Me] [Me] [Me]

21. 21R. L. Puurunen, Can. Chem. Conf., Ottawa, June 14, 2014
Conclusion
Source Puurunen, 2005 George, 2010 Knapas & Ritala,
2013
Explaination of
less-than-
monolayer GPC &
temp. trend
Quantitative Qualitative -
Description of
GPC change with
temperature
Decreases with
* decreasing [OH],
* [Me] ~constant
Decreases with
* decreasing [OH],
* decreasing [Me]
* n/z about
constant at 1.5
Change of surface
[Me] vs
temperature in
”background data”
[Me] [Me] [Me]
• Significant differences, which have remained
unnoticed so far?
• Me3Al/H2O is model system
 scientific discussion & agreement on the
basic trends needed
• New research activity welcome!

22. 22R. L. Puurunen, Can. Chem. Conf., Ottawa, June 14, 2014
2
Conformality

23. 23R. L. Puurunen, Can. Chem. Conf., Ottawa, June 14, 2014
Thin film conformality: one of the
fundamental advantages of ALD
Ritala et al.,
CVD 5 (1999) 7
Photo: Kalevala-koruSuntola; Lakomaa et al.
• #1 volume ALD application based on reactor sales
• Production: TiN-ZAZ-TiN, ZyALDTM (story, FinALD40)
Gutsche,FutureFabIntl.Issue14
George,plenarytalk,AVS-ALD2013
Catalysis
Silver
protection
DRAM
Suntola,
MRS Boston 1994
Microelectronics

24. 24R. L. Puurunen, Can. Chem. Conf., Ottawa, June 14, 2014
… but how deep exactly does the coating go?
… and how uniform is it?
Gordon et al.,
Chem. Vap.
Deposition
9 (2003) 73.
“small dose” “high dose”
Dendooven et al.,
J. Electrochem. Soc. 156
(2009) P63
”a”:
ALD Ru, AR 50/1 ALD TiN, AR 50/1
Detavernier, Tutorial, AVS-ALD conference, Kyoto, June 2014

25. 25R. L. Puurunen, Can. Chem. Conf., Ottawa, June 14, 2014
VTT: microscopic Si LHAR test structures for
ALD growth & conformality evaluation
25 mm
20mm
l
(side view)
l
g
Aspect ratios
Lateral length l (µm)
Gap (nm) 5000 1000 500 200 50 20
200 25000 5000 2500 1000 250 100
500 10000 2000 1000 400 100 40
1000 5000 1000 500 200 50 20
opening 100 80 60 40 20 10
opening
”PillarHall”
Gao et al., J. Vac. Sci. Technol. A 33 (2015) 010601.

26. 26R. L. Puurunen, Can. Chem. Conf., Ottawa, June 14, 2014
0
20
40
60
80
100
120
0 20 40 60 80 100 120
Thickness(nm)
Distance from port opening
Al2O3 ALD in PillarHall chips, 500 nm gap
VTT Micronova
• Full coverage up to
60 µm / AR ~120
• Thereafter linear decrease
Distance (µm) / AR
40 80 120 160 200 2400
Me3Al/H2O, PICOSUN R-150
300°C, 0.1 – 4 - 0.1 - 4 s sequence
Gao et al., J. Vac. Sci. Technol. A 33 (2015) 010601.

27. 27R. L. Puurunen, Can. Chem. Conf., Ottawa, June 14, 2014
TiO2 ALD in PillarHall chips, different gaps
VTT Micronova
• Slow initial decrease up to
~AR 80, steep decrease
from AR ~120 on
• Gap size affects the
results?
TiO2 at 110°C, ~100 nm
Gao et al., J. Vac. Sci. Technol. A 33 (2015) 010601.

28. 28R. L. Puurunen, Can. Chem. Conf., Ottawa, June 14, 2014
O2
O3 + H2
O2 long purge
* Automatic line scan: ~1 µm spot; GMRFILM
Max AR 10 000:1
Top-view SEM +
EDS line scan
Iridium ALD in PillarHall chip, 500 nm gap
University of Helsinki – Mattinen, Ritala ASM F120 reactor
250C
250C
185C
Ir(acac)3

29. 29R. L. Puurunen, Can. Chem. Conf., Ottawa, June 14, 2014
Conclusion, ALD conformality analysis
 PillarHall LHAR chips expose a new
parameter space for ALD modelling
 Up to AR 25000:1, molecular flow
 Sensitive detection of decay shapes
 Strong basis for modelling
Future ideas/Discussion:
 Line scan database for modelling? Interested parties for modelling?
Which parameters stored?
 Round Robin test for an ALD process?
 Process? Interested parties? HERALD?

30. 30R. L. Puurunen, Can. Chem. Conf., Ottawa, June 14, 2014
3 ”All men by nature desire to know”
Tuomo Suntola Aristotle
ALD History

31. 31R. L. Puurunen, Can. Chem. Conf., Ottawa, June 14, 2014
Virtual Project on the History of ALD (VPHA)
in atmosphere of Openness, Respect and Trust
 Volunteer-based effort: collect & read & summarize all early ALD
literature up to 1986
 Questions especially related to Molecular Layering,
also Atomic Layer Epitaxy
 Started in Summer 2013, to end summer 2016
 Uses cloud services & professional social media for fluent
collaboration
 Joint publications as outcomes
 Condition for participation: ability to work
in atmosphere of Openness, Respect and Trust
 LinkedIn group: ALD History
https://www.linkedin.com/groups/ALD-History-5072051/about

32. 32R. L. Puurunen, Can. Chem. Conf., Ottawa, June 14, 2014
Publication Plan v3 & outcomes
http://vph-ald.com/Publication%20Plan.html
1) Poster at Baltic ALD 2014 - done
2) Poster at ALD 2014, Kyoto - done
3) Presentation at ALD 2014, Kyoto - done
4) ALD history tutorial at ALD 2014, Kyoto – done
5) Essay on the early history of ALE-ALD – done
6) Website for ALD history and VPHA – done, http://vph-ald.com
7) Exhibition: 40 years of ALD in Finland - Photos, Stories (FinALD40) –
done
8) Review article/essay on the early history of ML-ALD - ongoing
9) Presentation at ALD 2016 - ongoing
10) Optional: general ALD history review article
11) Updating wikipedia
12) Closing the VPHA
Baltic ALD 2014 Helsinki
Baltic ALD 2015 Tartu
ALD Russia 2015 Moscow

33. 33R. L. Puurunen, Can. Chem. Conf., Ottawa, June 14, 2014
ALD History outlook:
VPHA looks for more participants
 There are now ~35 participants
 There are now 324 papers listed for up to 1986
 Each paper should be read by about three people
 we have to write roughly 1000 comments altogether
 We could have even 100 participants
 Your participation
is most welcome &
needed!
To participate, contact though
LinkedIn or email Riikka

34. 34R. L. Puurunen, Can. Chem. Conf., Ottawa, June 14, 2014
Acknowledgements
Funding: Academy of Finland,
Finnish Centre of Excellence on Atomic Layer Deposition
ALD conformality analysis test structures & analysis:
 VTT: Gao Feng, Meeri Partanen, Jaana Marles, Antti Tolkki
 University of Helsinki: Miika Mattinen, Mikko Ritala
ALD history
 Tuomo Suntola, Anatoly Malygin, Jonas Sundqvist
 All participants of VPHA (>30)
 American Vacuum Society (announcements, tutorial)
Contact:
riikka.puurunen@ vtt.fi

35. 35R. L. Puurunen, Can. Chem. Conf., Ottawa, June 14, 2014
Thank You!
Atomikerroskasvatus
‫השקעת‬ ‫אטומיות‬ ‫שכבות‬
εναπόθεση ατομικού στρώματος
Atomlagenabscheidung
Parmanu Parat Nishepan
परमाणु परत निक्षेपण
Deposizione a Strati Atomici
原子層堆積
원자층증착
आण्विक थर लेप
Atomlagsdeponering
атомно-слоевое осаждение
Dépôt de Couches Atomiques
Dépôt Chimique en Phase Vapeur à Flux Alternés
Atomlagerdeponering
Atomik Katman Biriktirme
Oсадження атомних шарів
Aatomkihtsadestus
Depositación de Capas Atómicas
Atomic Layer Deposition Atoomlaagdepositie
原子层沉积
Deposição por Camadas Atômicas
ALD name collection in LinkedIn ALD – Atomic Layer Deposition
Mолекулярное Hаслаивание

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