Invited talk by R.L. Puurunen "Recent Progress in Analysis of the Conformality of Films by Atomic Layer Deposition" at AVS69, Portland, Oregon, Nov 5-10, 2023, https://avs69.avs.org/. ABSTRACT. Conformality is a fundamental characteristic of atomic layer deposition (ALD) thin film growth technique. “Conformal” film refers to a film that covers all surfaces of a complex three-dimensional substrate with everywhere the same thickness and properties. ALD - invented independently by two groups in 1960s and 1970s - has since late 1990s been transformational in semiconductor technology. Apart from semiconductors, conformal ALD films find applications and interest in widely varied fields such as microelectromechanical systems, pharmaceutical powder processing, optical coatings, battery technologies and heterogeneous catalysts. Conformality follows directly from the “ideal ALD” principles: growth of material through the use of repeated separate self-terminating (i.e., saturating and irreversible) gas-solid reactions of at least two compatible reactants on a solid surface. Obtaining conformality in practice is not self-evident, however. Reasons for deviation from conformality are multiple, ranging from mass transport limitations to slow reaction kinetics and various deviations from ideal ALD (e.g., by-product reactivity or a continuous chemical vapor deposition (CVD) component through reactant decomposition or insufficient purging). Incomplete conformality can also be intentional: a saturation profile inside a feature can be exposed, to enable an analysis of kinetic parameters of the reactions. This invited talk will explore recent progress especially by the author and collaborators in understanding ALD conformality and kinetics, obtained via experiments and simulations. Experiments have been made with the recently commercialized (chipmetrics.com) silicon-based PillarHallTM lateral HAR test chips (channel height ~500 nm) and spherical mesoporous high-surface-area materials (average pore diameter ~10 nm, sphere diameter ~1 mm). Simulations are presented for 1d feature-scale models and optionally a recently developed 3d code for spheres. Two codes are available on GitHub: DReaM-ALD (diffusion-reaction model, DRM) and Machball (ballistic transport-reaction model, BTRM). Often it is assumed that diffusion during an ALD process in HAR features is by Knudsen diffusion and free molecular flow conditions prevail (Kn >>1). If so, a characteristic “fingerprint saturation profile” can be obtained, and the slope method (derived for DRM-ALD-Arts, GitHub) can be used to back-extract the lumped sticking coefficient. When diffusion is in the transition flow (Kn ~1) or continuum flow (Kn<<1), the shape of the saturation profile depends on process conditions and the slope method is not applicable.

1. Puurunen and coworkers, ALD 2023, Jul 23-26, 2023, Bellevue, Washington
Riikka L. Puurunen
Aalto University, School of Chemical Engineering,
Department of Chemical and Metallurgical Engineering
Recent Progress in
Analysis of the
Conformality of Films
by Atomic Layer
Deposition
AVS 69, Nov 5-10, 2023
Portland, Oregon, USA
From
pillarhall.com,
accessed
5.11.2023.
Photo credit:
Riikka Puurunen
& Mari
Laamanen;
edited by VTT
rA
rI
Open Science

2. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
Why conformality studies?
Semiconductor devices need (new) thin films
of ever better conformality
● Initial process development
● Compare processes & choose best
● Compare tools & vendors
● Understand processes (kinetics!)
→ model & simulate processes &
tools
● …
Ovanesyan et al., J. Vac. Sci. Technol. A 37 (2019)
060904; DOI:10.1116/1.5113631 (CC BY)
1.

3. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
Brief historical perspective: ALD conformality studies
Suntola, MRS fall
meeting 1994, Boston, MA,
USA. Figure in:
DOI:10.1002/cvde.201402012
Ritala et al., Chem. Vap.
Deposition 5 (1999) 7-9;
DOI:10.1002/(SICI)1521-
3862(199901)5:1<7::AID-
CVDE7>3.0.CO;2-J
Gordon et al., Chem. Vap.
Deposition 9 (2003) 73-78;
DOI:10.1002/cvde.200390005
Dendooven et al.,
J. Electrochem. Soc. 156
(2009) P64-P67;
DOI:10.1149/1.3072694
Also: porous high-surface-area materials
AR
~5:1
AR
43:1
Gao et al., J. Vac. Sci.
Technol. A. 33 (2015)
010601;
DOI:10.1116/1.4903941
AR
100:1
AR
25,000:1
step
Haukka, Lakomaa, Suntola, Stud. Surf.
Chem. Catal. 120 Part A (1999) 715–750;
DOI:10.1016/S0167-2991(99)80570-9
Gayle et al., Chem. Mater. 33 (2021) 5572–5583;
DOI:10.1021/acs.chemmater.1c00770
AR
>60,000:1
1.

4. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
Brief historical perspective: ALD conformality studies
Suntola, MRS fall
meeting 1994, Boston, MA,
USA. Figure in:
DOI:10.1002/cvde.201402012
Ritala et al., Chem. Vap.
Deposition 5 (1999) 7-9;
DOI:10.1002/(SICI)1521-
3862(199901)5:1<7::AID-
CVDE7>3.0.CO;2-J
Gordon et al., Chem. Vap.
Deposition 9 (2003) 73-78;
DOI:10.1002/cvde.200390005
Dendooven et al.,
J. Electrochem. Soc. 156
(2009) P64-P67;
DOI:10.1149/1.3072694
Also: porous high-surface-area materials
Gao et al., J. Vac. Sci.
Technol. A. 33 (2015)
010601;
DOI:10.1116/1.4903941
step
Haukka, Lakomaa, Suntola, Stud. Surf.
Chem. Catal. 120 Part A (1999) 715–750;
DOI:10.1016/S0167-2991(99)80570-9
Gayle et al., Chem. Mater. 33 (2021) 5572–5583;
DOI:10.1021/acs.chemmater.1c00770
1.
Review, new term
proposed: Hole-
equivalent aspect
ratio (EAR)
Cremers, Puurunen,
Dendooven, Appl. Phys.
Rev. 6 (2019) 021302;
DOI:10.1063/1.5060967
AR
~5:1
EAR
~2.5:1
AR
43:1
EAR
43:1
AR
100:1
EAR
50:1
AR
25,000:1
EAR
12,500:1
AR
>60,000:1
EAR
>60,000:1

5. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
Brief historical perspective: kinetic/conformality modelling
1.
There are many more papers, see review:
Cremers, Puurunen, Dendooven, Appl. Phys. Rev. 6 (2019)
021302; DOI:10.1063/1.5060967
Macball
April 2020

6. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
New terminology for ALD saturation (/thickness) profiles
Yim, Ylivaara et al., Phys. Chem. Chem. Phys. 22
(2020) 23107-23120; DOI:10.1039/D0CP03358H
1.
Dimensionless distance x̃ = x/H
(a) as-measured:
Ylilammi et al., 2018
(b) scaled:
Yim et al., 2020
(c) Type 1 normalized:
e.g. Arts et al., 2019
(d) Type 2 normalized:
Many earlier publications
Speaker’s
favourite

7. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
Contents
1. Introduction to conformality studies (done already)
2. Some modelling fundamentals
○ Atomic layer deposition, mean free path & Knudsen
number (diffusion regimes), Langmuir adsorption,
modelling of reactant transport
3. PillarHallTM LHAR conformality analysis concept
4. Recent progress - experiments, results
5. Outlook
+ Plenty of extra materials

8. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
Atomic
layer
deposition
(ALD)
Van Ommen,
Goulas, Puurunen,
“Atomic layer
deposition” in
Kirk-Othmer
Encyclopedia of
Chemical
Technology, 2021,
https://doi.org/10.10
02/0471238961.koe
00059
Images in
Wikimedia
Commons
Repeated
self-
terminating
gas-solid
reactions
2.

9. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
Knudsen number reveals the diffusion regime
Mean free path (λ)
From kinetic theory of gases
2.
Collision cross section
σi,j = π ( ri + rj )2 *
Knudsen number
Kn = λ / h
* Mistake in this formula (Eq. 4) of DOI:10.1063/1.5060967 , correction in
footnote (**) of Yim, Verkama et al., Phys. Chem. Chem. Phys. 24 (2022)
8645-8660; DOI:10.1039/D1CP04758B .
Kn >>1
Free molecular flow
(Knudsen diffusion)
Kn ~1
Transition regime
Kn <<1
Continuum
(molecular diffusion)
rA
rI
By A. Greg (Greg L at English Wikipedia) -
Own work, Public Domain,
https://commons.wikimedia.org/w/index.php?c
urid=1325234
A = Reactant A
I = Inert

10. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
Langmuir
adsorption
2.
Van Ommen, Goulas, Puurunen,“Atomic layer deposition” in Kirk-Othmer Encyclopedia of Chemical
Technology, 2021, https://doi.org/10.1002/0471238961.koe00059. Images courtesy of Arts and co-workers.
A + * ⇌ A*
Reaction rate equation
Järvilehto et al. Phys. Chem.
Chem. Phys. 25 (2023) 22952-
22964;
DOI:10.1039/D3CP01829F
Diffusion-limited hT > 1 Reaction-limited hT << 1
Thiele modulus hT =
adsorption rate
diffusion rate

11. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
Reactant transport in HAR features
Fick’s law of diffusion Ballistic transport
Monte Carlo
2.
Poodt et al., J. Vac. Sci. Technol. A 35 (2017)
021502; DOI:10.1116/1.4973350
Järvilehto et al. Phys. Chem. Chem. Phys. 25 (2023) 22952-22964; DOI:10.1039/D3CP01829F
Original papers:
Ylilammi et al., J. Appl. Phys. 123 (2018) 205301; DOI:10.1063/1.5028178
Yanguas-Gil and J. W. Elam, Theor. Chem. Acc. 133 (2014) 1465; DOI:10.1007/s00214-014-1465-x
Kn >>1
Kn: any
Kn: any

12. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
~Ten years of PillarHallTM LHAR
www.pillarhall.com
1st gen prototype [ 2nd gen ] 3rd gen, LHAR3 4th gen, LHAR4
Tekes (Business Finland) proj. PillarHall
Academy of Finland (now Research Council of Finland) proj. ALDCoE
Trademark ~2015
PillarHallTM
Customers, investors etc. → →
www.chipmetrics.com
Dr. Mikko Utriainen
Puurunen
Professor
2017 →
Aalto
Univ.
2 scientific articles
1st: Gao et al. 2015
DOI:10.1116/1.4903941
[ 0 articles ]
>20 scientific articles for LHAR3+LHAR4
“LHAR3 core paper”: Yim, Ylivaara et al., 2020
DOI:10.1039/D0CP03358H
ALD Stories
Podcast Ep. 14
3.

13. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
PillarHallTM LHAR conformality analysis concept
1 Optical analysis
through membrane
2 Membrane removed,
surface exposed for analysis
Kia et al.,
Nanomaterials,
2019,
DOI:10.3390/nan
o9071035
Reflectometer line scans
Yim, Ylivaara et al.,
PCCP, 2020,
DOI:10.1039/D0CP03358H
3.

14. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
PillarHallTM LHAR: measurement vs. simulation
Yim, Ylivaara, Ylilammi, Korpelainen, Haimi, Verkama, Utriainen, Puurunen, Saturation profile based conformality analysis
for atomic layer deposition: aluminum oxide in lateral high-aspect-ratio channels,
Phys. Chem. Chem. Phys. 22 (2020) 23107-23120; DOI:10.1039/D0CP03358H
Measurement Simulation (Ylilammi model)
TMA + water
300°C
3.
as-measured Type 1 norm.
scaled as-measured Type 1 norm.
scaled

15. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
Recent progress – experiments, results
4.

16. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
Effect of varied parameters on thickness profile (1/2)
E.g.: Penetration depth ~∝ (GPC)-1
Yim, Ylivaara et al.,
TMA-water,
Phys. Chem. Chem.
Phys., 22 (2020)
23107-23120;
DOI:10.1039/D0CP0
3358H
● Observed experimentally
○ Mattinen et al., Ir processes
Langmuir 32 (2016) 10559–10569;
DOI:10.1021/acs.langmuir.6b03007
Yim, Verkama, Velasco, Arts, Puurunen, Phys. Chem. Chem. Phys. 24
(2022) 8645-8660; DOI https://doi.org/10.1039/D1CP04758B
4.

17. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
Effect of varied parameters on thickness profile (2/2)
Comparison of diffusion regimes
Kn >> 1
Free molecular flow
Kn ~ 1
Transition regime
Yim, Verkama et al.,
Phys. Chem. Chem. Phys. 24
(2022) 8645-8660; DOI
https://doi.org/1
0.1039/D1CP04758B
DReaM-ALD
4.

18. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
Saturation profile contains
kinetic information
Ylilammi, Ylivaara, Puurunen, J. Appl. Phys. 123 (2018) 205301; DOI:10.1063/1.5028178
4.

19. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
Arts et al. slope method* to back-extract sticking coefficient
Arts, Vandalon, Puurunen, Utriainen, Gao, Kessels,
Knoops, J. Vac. Sci. Technol. A (2019) 37;
DOI: 10.1116/1.5093620
*Name “slope method” in use since Yim et al., Phys. Chem. Chem. Phys., 24 (2022) 8645-8660: DOI:10.1039/D1CP04758B
● Slope method based on Yanguas-Gil & Elam DR
model, implemented by Arts (drm-ald-arts)
● Requires Kn >>1
● Other works show similar trends
4.
Yim, Verkama, Velasco, Arts,
Puurunen, Phys. Chem.
Chem. Phys. 24 (2022) 8645-
8660;
DOI:10.1039/D1CP04758B

20. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
For PEALD, penetration depth → info on plasma
Arts et al. “penetration depth method” Kn >>1
Arts, Utriainen, Puurunen, Kessels, Knoops, J. Phys. Chem. C,
123 (2019) 27030-27035; DOI:10.1021/acs.jpcc.9b08176
Van de Poll et al., Appl. Phys. Lett. 123 (2023) 182902;
DOI:10.1063/5.0168768
“Recombination probabilities of oxygen radicals at
atmospheric pressure are extracted to be
4×10−4 for SiO2 and 6×10−5 for TiO2.”
Just out! Published Online: 31 October 2023
Kn ~ 1
4.

21. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
Open-science-enabled quantitative comparison of
diffusion–reaction and ballistic transport–reaction models
Järvilehto, Velasco, Yim, Gonsalves,
Puurunen, Phys. Chem. Chem. Phys.
25 (2023) 22952-22964;
DOI:10.1039/D3CP01829F 1. Penetration depth: DR < BTR model
2. Slope: DR > BTR model
: DReaM-ALD, Machball
3.
Kn >>1
4.
DR BTR

22. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
More of Open Science? ALD saturation profile database?
https://zenodo.org/communities/ald-saturation-profile-open-data
Open Data makes the reuse of data easier
– and more reliable
● Example: Aguinsky et al., Solid State Electronics 201
(2023) 108584;
https://doi.org/10.1016/j.sse.2022.108584
4.
?
3

23. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
Investigation of unwanted CVD component in ALD
Monte Carlo simulations
Cremers, Puurunen, Dendooven, Conformality in atomic layer
deposition: Current status overview of analysis and modelling, Appl.
Phys. Rev. 6 (2019) 021302; DOI:10.1063/1.5060967
1. Reactant decomposition (non-
saturating reaction with self)
modelled
2. Mixing of reactants in gas
phase?
No systematic experimental
investigations published (?)
time
4.

24. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
● Pristine territory for scientific
advances
● Measurement of experimental
saturation profiles
● Modelling of saturation profiles
○ Model development
○ Kinetic parameter extraction
● Open Science
→ global collaboration
○ Zenodo.org saturation profile community
co-curator? (academic?)
Outlook – what’s next?
5.
Open Science

25. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
Acknowledgements
All collaborators throughout the years
5.
Catalysis group at Aalto University (May 2023)

26. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
Extra materials in this slideset, with links
1. Publications from http://pillarhall.com/references.htm, accessed 7.11.2023
2. Fundamentals of atomic layer deposition: an introduction (“ALD 101”) presentation at ALD
2021
3. ALD Stories Episode 14: Understanding Conformality with Riikka Puurunen
4. Introductory ALD chapter in Kirk-Othmer Encyclopedia of Chemical Technology (many
creative commons images)
5. On the fundamentals of ALD: the importance of getting the picture right, by Riikka L.
Puurunen and J. Ruud van Ommen
6. Video derivation of the well-known Langmuir equation
7. Järvilehto et al. presentation at ALD 2023
8. Records on how research code was published to GitHub and linked to Zenodo.org
9. ALD contents at openlearning.aalto.fi
10. Virtual Project on the History of ALD (VPHA)
11. Abstract of this invited talk
extras

27. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
Scientific articles created with PillarHall®
microscopic lateral high-aspect-ratio (LHAR)
test structures
From http://pillarhall.com/references.htm, accessed 7.11.2023
Simulation of conformality of ALD growth inside lateral channels: comparison
between a diffusion–reaction model and a ballistic transport–reaction model,
Jänis Järvilehto, Jorge A. Velasco, Jihong Yim, Christine Gonsalves and Riikka
L. Puurunen, ChemRxiv. Cambridge: Cambridge Open Engage, 2023,
https://doi.org/10.26434/chemrxiv-2023-bnzgr
3D Thin Film Metrology without Cross-Sectional Sampling (2023), Anish Philip,
Mikko Utriainen, Thomas Werner, Pasi Hyttinen, Jaakko Saarilahti, Jussi
Kinnunen, Feng Gao, IEEE International Interconnect Technology Conference
(IITC) and IEEE Materials for Advanced Metallization Conference
(MAM)(IITC/MAM), https://doi.org/10.1109/IITC/MAM57687.2023.10154886
Characterization of PillarHall test chip structures using a reflectometry
technique, Aleksandr Danilenko et al 2023 Meas. Sci. Technol. 34 094006,
http://urn.fi/URN:ISBN:978-952-64-1265-8
Atomic/molecular layer deposited crystalline metal-organic thin films based on
low-valent metals, Jenna Multia, Aalto University publication series Doctoral
Theses 69/2023, http://urn.fi/URN:ISBN:978-952-64-1265-8
Molecular layer deposition of alucone in high aspect ratio trenches: The effect of
TMA outgassing on step-coverage, H. Jain, M. Creatore and P. Poodt, J. Vac.
Sci. Technol.A 41 (2023), 012401, https://doi.org/10.1116/6.0002249
Conformality of atomic layer deposition in microchannels: impact of process
parameters on the simulated thickness profile, J. Yim, E. Verkama, J. Velasco,
K. Arts and R.L. Puurunen, Phys. Chem. Chem. Phys. (2022),
https://doi.org/10.1039/D1CP04758B
Optical metrology of 3D thin film conformality by LHAR chip assisted method M.
Utriainen, K. Saastamoinen, H. Rekola, O.M.E. Ylivaara, R.L. Puurunen and
P.Hyttinen, Proceedings Volume 12008, Photonic Instrumentation Engineering
IX; 120080D (2022), Event: SPIE OPTO, 2022, San Francisco, California,
United States, https://doi.org/10.1117/12.2609643
Conformality and the role of ions during plasma-assisted atomic layer
deposition, K. Arts (2021), PhD thesis 1 (Research TU/e/ Graduation TU/e),
Applied Physics and Science Education, Eindhoven University of Technology,
20210915_CO_Arts_hf.pdf (tue.nl)
Impact of Ions on Film Conformality and Crystallinity during Plasma-Assisted
Atomic Layer Deposition of TiO2, K. Arts, H. Thepass, M.A. Verheijen, R.L.
Puurunen, W.M.M. Kessels and H.C.M. Knoops, Chem. Mater. (2021),
https://doi.org/10.1021/acs.chemmater.1c00781
Saturation profile measurement of atomic layer deposited film by X-ray
microanalysis on lateral high-aspect-ratio structure, E. Haimi, O.M.E. Ylivaara,
J. Yim and R.L. Puurunen, Appl. Surf. Sci. Advances 5 (2021), 100102,
https://doi.org/10.1016/j.apsadv.2021.100102
Oxygen Recombination Probability Data for Plasma-Assisted Atomic Layer
Deposition of SiO2 and TiO2, K. Arts, S. Deijkers, R.L. Puurunen, W.M.M.
Kessels and H.C.M. Knoops, J. Phys. Chem. C 2021, 125, 15, 8244–8252,
https://doi.org/10.1021/acs.jpcc.1c01505
Saturation Profile Based Conformality Analysis for Atomic Layer Deposition:
Aluminum Oxide in Lateral High-Aspect-Ratio Channels, J. Yim, O.M.E.
Ylivaara, M. Ylilammi, V. Korpelainen, E. Haimi, E. Verkama, M. Utriainen and
R. L. Puurunen, Phys. Chem. Chem. Phys. 22 (2020), 23107,
https://doi.org/10.1039/D0CP03358H
Two-Step Approach for Conformal Chemical Vapor-Phase Deposition of Ultra-
Thin Conductive Silver Films, S. Wack, P.L. Popa, N. Adjeroud, C. Vergne and
R. Leturcq, ACS Appl. Mater. Interfaces 12 (2020), 32, 36329–36338,
https://doi.org/10.1021/acsami.0c08606
Evidence for low-energy ions influencing plasma-assisted atomic layer
deposition of SiO2: impact on the growth per cycle and wet etch rate, K. Arts,
J.H. Deijkers, T. Faraz, R.L. Puurunen, W.M.M. (Erwin) Kessels and H.C.M.
Knoops, Appl. Phys. Lett. 117 (2020), 031602,
https://doi.org/10.1063/5.0015379
Film Conformality and Extracted Recombination Probabilities of O Atoms during
Plasma-Assisted Atomic Layer Deposition of SiO2, TiO2, Al2O3, and HfO2, K.
Arts, M. Utriainen, R. L. Puurunen, W. M. M. Kessels, H. C. M. Knoops, J. Phys.
Chem. C 123 (2019), 44, 27030-27035,
https://pubs.acs.org/doi/10.1021/acs.jpcc.9b08176
ToF-SIMS 3D Analysis of Thin Films Deposited in High Aspect Ratio Structures
via Atomic Layer Deposition and Chemical Vapor Deposition, A. M. Kia, N.
Haufe, S. Esmaeili, C. Mart, M. Utriainen, R. L. Puurunen, W. Weinreich,
Nanomaterials 9 (2019) art. 1035; https://doi.org/10.3390/nano9071035
Surface-Inhibiting Effect in Chemical Vapor Deposition of Boron–Carbon Thin
Films from Trimethylboron, L. Souqui, H. Högberg and H. Pedersen, Chem.
Mater. 31 (2019) 5408-5412; https://doi.org/10.1021/acs.chemmater.9b0049
Sticking probabilities of H2O and Al(CH3)3 during atomic layer deposition of
Al2O3 extracted from their impact on film conformality, K. Arts, V. Vandalon,
R.L. Puurunen, M. Utriainen, F. Gao, W.M.M. Kessels, H.C. Knoops, J. Vac. Sci.
Technol. A 37 (2019) art. 030908; https://doi.org/10.1116/1.5093620
Conformality in atomic layer deposition: current status overview of analysis and
modelling, V. Cremers, R.L. Puurunen, J. Dendooven, Appl. Phys. Rev. 6
(2019) art. 021302; https://doi.org/10.1063/1.5060967
Modeling growth kinetics of thin films made by atomic layer deposition in lateral
high-aspect-ratio structures, M. Ylilammi, O. M. E. Ylivaara, R. L. Puurunen, J.
Appl. Phys. 123 (2018) art. 205301 (8 pages).
https://doi.org/10.1063/1.5028178
Influence of ALD temperature on thin film conformality: Investigation with
microscopic lateral high-aspect-ratio structures, R. L. Puurunen, F. Gao,
Proceedings of the International Baltic Conference on Atomic Layer Deposition,
2-4 Oct 2016, St. Petersburg, Russia. Electronically published in IEEE Xplore,
http://ieeexplore.ieee.org/document/7886526/
Nucleation and Conformality of Iridium and Iridium Oxide Thin Films Grown by
Atomic Layer Deposition, M. Mattinen, J. Hämäläinen, F. Gao, P. Jalkanen, K.
Mizohata, J. Räisänen, R. L. Puurunen, M. Ritala, M. Leskelä, Langmuir 32
(2016) 10559, http://dx.doi.org/10.1021/acs.langmuir.6b03007
Microscopic silicon-based lateral high-aspect-ratio structures for thin film
conformality analysis, F. Gao, S. Arpiainen, R. L. Puurunen, J. Vac. Sci.
Technol. A 33 (2015) 010601, http://dx.doi.org/10.1116/1.4903941
extras

28. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
https://youtu.be/xOYrCjcVTzA?si=1djvKC
Gx4AkFfzoU
(INVITED) Fundamentals of atomic layer
deposition: an introduction (“ALD 101”)
ABSTRACT:
Atomic layer deposition (ALD) has become of global importance
as a processing technology for example in semiconductor device
fabrication, and its application areas are continuously expanding.
The significance of ALD was highlighted e.g. by the recent
(2018) Millennium Technology Prize. Tens of companies are
offering ALD tools, and thousands of people are involved in ALD
R&D globally. A continuous need exists to educate new people
on the fundamentals of ALD.
While ALD for manufacturing may be regarded mature, as a
scientific field, ALD—in the author’s view—is developing. For
example, understanding of the early history of ALD is evolving,
related to the two independent inventions of ALD under the
names Atomic Layer Epitaxy in the 1970s and Molecular
Layering in the 1960s [1-4]. Also, significantly varying views exist
in the field related to the description and meaningfulness of even
some core ALD concepts [5].
<continues…>
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29. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
Back to Basics: Understanding Conformality with Riikka Puurunen – ALD Stories Ep. 14
https://beneq.com/en/podcasts/
https://youtu.be/icb1xEf4eCQ?si=KshALwIrCDAk-vxL
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30. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
Abstract: Atomic layer deposition (ALD) is a gas-phase method to grow layers of
solid materials with subnanometer precision. It has been invented independently in
the Soviet Union in the 1960s under the name molecular layering, and in the
1970s in Finland under the name atomic layer epitaxy. ALD relies on alternatingly
exposing a surface to gaseous reactants—separated by a purge step—that react
in a self-terminating manner. This article introduces the fundamentals of the
surface chemistry of ideal ALD, including saturating and irreversible reactions,
growth per cycle, monolayer concepts relevant to ALD, typical surface reaction
mechanisms, saturation-limiting factors, growth modes, area-selective ALD,
growth kinetics, and conformality. It also discusses typical deviations from ideal
ALD. Over the years, many different ALD process chemistries have been
developed. A range of reactor systems is available, depending on the type of
substrate and required productivity. ALD is broadly applicable in practice since it
couples nanoscale precision with a good scalability and can be used to deposit a
large variety of materials. In recent years, the interest in ALD has been growing
strongly. The most important sector regarding commercial applications of ALD is
currently the semiconductor industry.
Van Ommen, Goulas,
Puurunen,
“Atomic layer
deposition” in
Kirk-Othmer
Encyclopedia of
Chemical Technology,
2021,
https://doi.org/10.1002/0
471238961.koe00059
Many images in Wikimedia Commons
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31. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
extras
● https://www.slideshare.net/RiikkaPuurunen/on-the-fundamentals-
of-ald-the-importance-of-getting-the-picture-right-by-puurunen-
and-van-ommen
● https://youtu.be/jqm_wf49WwM
● https://aalto.cloud.panopto.eu/Panopto/Pages/Viewer.aspx?id=13
ed854b-5df8-4d37-8ff1-ac0d00dde319
Title: On the fundamentals of ALD: the
importance of getting the picture right
Authors: Riikka L. Puurunen and J. Ruud
van Ommen
Session: Precursors and Chemistry:
Simulation, Modeling, and Theory of ALD

32. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
Prof. Puurunen Lightboard 1 - Single-site Langmuir
adsorption isotherm derivation
● https://youtu.be/KddVM4nx
gwI?si=s-nm0iZ5j7lED-Rs
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33. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
● https://aalto.cloud.panopto.
eu/Panopto/Pages/Viewer.a
spx?id=0fec7dbe-fedf-
41de-a576-b06901010532
Article since then published:
Järvilehto, Velasco, Yim, Gonsalves, Puurunen,
Simulation of conformality of ALD growth inside
lateral channels: comparison between a diffusion–
reaction model and a ballistic transport–reaction
model, Phys. Chem. Chem. Phys. 25 (2023) 22952-
22964; DOI:10.1039/D3CP01829F
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34. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
Records on how research code was published to GitHub
and linked to Zenodo.org
The Catalysis research group has published its first-ever open code! Coined DReaM-ALD, the recently
published Matlab script provides an implementation of a diffusion–reaction model developed by Ylilammi et al.
(J. Appl. Phys. 123, 205301 (2018), DOI: 10.1063/1.5028178). The model simulates atomic layer deposition in
high-aspect-ratio structures and generates saturation profiles, which show how the film thickness evolves with
penetration into the structure. This Matlab implementation was originally written by Emma Verkama in 2019 by
request of Prof. Riikka Puurunen, and the code was later published by Jänis Järvilehto. In addition to Github,
the code was also made available on Zenodo.
There was a significant delay (~3 years) between the creation and publication of the code. As there was no
prior history of open code in the group, the barrier to publication was relatively high. Questions, such as…
Where should we publish the code? What kind of information would be useful for a potential user? How does
the process work in general? Where do I click???
…may arise. While the best practices may seem obvious to a software engineer, generating research code
can be a messy affair in other fields. …
https://blogs.aalto.fi/catprofopen/2023/04/12/catalysis-
research-group-publishes-diffusion-reaction-model-code/
12.04.2023 Written by Jänis Järvilehto
https://youtu.be/ksxAIaytv68?si=qw
Edi47Vr6BAFhti
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35. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
ALD contents at openlearning.aalto.fi
https://openlearni
ng.aalto.fi/course/
view.php?id=100
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36. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
Scientific journal articles from VPHA:
1. Essay: R. L. Puurunen, "A Short History of Atomic Layer Deposition: Tuomo Suntola's Atomic Layer Epitaxy", Chemical
Vapor Deposition 20 (2014) 332-344. DOI: 10.1002/cvde.201402012. Open Access.
2. Essay: A. A. Malygin, V. E. Drozd, A. A. Malkov, V. M. Smirnov: "From V. B. Aleskovskii’s "Framework" Hypothesis to
the Method of Molecular Layering/Atomic Layer Deposition", Chemical Vapor Deposition 21 (2015) 216-240. DOI:
10.1002/cvde.201502013.
3. Review article: “Recommended reading list of early publications on atomic layer deposition—Outcome of the “Virtual
Project on the History of ALD””, Esko Ahvenniemi, Andrew R. Akbashev, Saima Ali, Mikhael Bechelany, Maria
Berdova, Stefan Boyadjiev, David C. Cameron, Rong Chen, Mikhail Chubarov, Veronique Cremers, Anjana Devi,
Viktor Drozd, Liliya Elnikova, Gloria Gottardi, Kestutis Grigoras, Dennis M. Hausmann, Cheol Seong Hwang, Shih-Hui
Jen, Tanja Kallio, Jaana Kanervo, Ivan Khmelnitskiy, Do Han Kim, Lev Klibanov, Yury Koshtyal, A. Outi I. Krause,
Jakob Kuhs, Irina Kärkkänen, Marja-Leena Kääriäinen, Tommi Kääriäinen, Luca Lamagna, Adam A. Łapicki, Markku
Leskelä, Harri Lipsanen, Jussi Lyytinen, Anatoly Malkov, Anatoly Malygin, Abdelkader Mennad, Christian Militzer, Jyrki
Molarius, Małgorzata Norek, Çağla Özgit-Akgün, Mikhail Panov, Henrik Pedersen, Fabien Piallat, Georgi Popov, Riikka
L. Puurunen, Geert Rampelberg, Robin H. A. Ras, Erwan Rauwel, Fred Roozeboom, Timo Sajavaara, Hossein Salami,
Hele Savin, Nathanaelle Schneider, Thomas E. Seidel, Jonas Sundqvist, Dmitry B. Suyatin, Tobias Törndahl, J. Ruud
van Ommen, Claudia Wiemer, Oili M. E. Ylivaara, Oksana Yurkevich, Journal of Vacuum Science and Technology A
35 (2017) 010801 (13 pages). DOI: 10.1116/1.4971389. Open access.
4. Proceedings article: R. L. Puurunen, "Learnings from an Open Science Effort: Virtual Project on the History of ALD",
ECS Transactions 86(6) (2018) 3-17; doi:10.1149/08606.0003ecst. Open access preprint, DOI: 10.1149/osf.io/exyv3.
https://vph-ald.com/ (materials available as of November 2023, no new activities to come)
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37. Puurunen - invited, AVS 69, Nov 5-10, 2023, Portland, Oregon
Recent Progress in Analysis of the Conformality of Films
by Atomic Layer Deposition
Author: Prof. Riikka Puurunen, Aalto University, Finland
Topic: Atomic Scale Processing Mini-Symposium, Session: AP7+TF: Novel ALD/CVD Precursors and Processes for High Aspect Ratio Architectures
Invited Paper: Yes
ABSTRACT. Conformality is a fundamental characteristic of atomic layer deposition (ALD) thin film growth technique. “Conformal” film refers to a film that covers all
surfaces of a complex three-dimensional substrate with everywhere the same thickness and properties. ALD - invented independently by two groups in 1960s and
1970s - has since late 1990s been transformational in semiconductor technology. Apart from semiconductors, conformal ALD films find applications and interest in
widely varied fields such as microelectromechanical systems, pharmaceutical powder processing, optical coatings, battery technologies and heterogeneous
catalysts.
Conformality follows directly from the “ideal ALD” principles: growth of material through the use of repeated separate self-terminating (i.e., saturating and irreversible)
gas-solid reactions of at least two compatible reactants on a solid surface. Obtaining conformality in practice is not self-evident, however. Reasons for deviation from
conformality are multiple, ranging from mass transport limitations to slow reaction kinetics and various deviations from ideal ALD (e.g., by-product reactivity or a
continuous chemical vapor deposition (CVD) component through reactant decomposition or insufficient purging). Incomplete conformality can also be intentional: a
saturation profile inside a feature can be exposed, to enable an analysis of kinetic parameters of the reactions.
This invited talk will explore recent progress especially by the author and collaborators in understanding ALD conformality and kinetics, obtained via experiments and
simulations. Experiments have been made with the recently commercialized (chipmetrics.com) silicon-based PillarHallTM lateral HAR test chips (channel height ~500
nm) and spherical mesoporous high-surface-area materials (average pore diameter ~10 nm, sphere diameter ~1 mm). Simulations are presented for 1d feature-
scale models and optionally a recently developed 3d code for spheres. Two codes are available on GitHub: DReaM-ALD (diffusion-reaction model, DRM) and
Machball (ballistic transport-reaction model, BTRM). Often it is assumed that diffusion during an ALD process in HAR features is by Knudsen diffusion and free
molecular flow conditions prevail (Kn >>1). If so, a characteristic “fingerprint saturation profile” can be obtained, and the slope method (derived for DRM-ALD-Arts,
GitHub) can be used to back-extract the lumped sticking coefficient. When diffusion is in the transition flow (Kn ~1) or continuum flow (Kn<<1), the shape of the
saturation profile depends on process conditions and the slope method is not applicable.
extras