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Puurunen & Van Ommen, ALD 2020 online conference 29.6.-1.7.2020, pre-recorded poster talk (18.6.2020)
Riikka L. Puurunena
...
Puurunen & Van Ommen, ALD 2020 online conference 29.6.-1.7.2020, pre-recorded poster talk (18.6.2020)
2
EuroCVD 22 - Balti...
Puurunen & Van Ommen, ALD 2020 online conference 29.6.-1.7.2020, pre-recorded poster talk (18.6.2020)
Critical discussion
...
Puurunen & Van Ommen, ALD 2020 online conference 29.6.-1.7.2020, pre-recorded poster talk (18.6.2020)
Outline
• Introducti...
Puurunen & Van Ommen, ALD 2020 online conference 29.6.-1.7.2020, pre-recorded poster talk (18.6.2020)
ALD cartoons over th...
Puurunen & Van Ommen, ALD 2020 online conference 29.6.-1.7.2020, pre-recorded poster talk (18.6.2020)
Ideal ALD – one mono...
Puurunen & Van Ommen, ALD 2020 online conference 29.6.-1.7.2020, pre-recorded poster talk (18.6.2020)
https://en.wikipedia...
Puurunen & Van Ommen, ALD 2020 online conference 29.6.-1.7.2020, pre-recorded poster talk (18.6.2020)
https://en.wikipedia...
Puurunen & Van Ommen, ALD 2020 online conference 29.6.-1.7.2020, pre-recorded poster talk (18.6.2020)
Ideal ALD - saturati...
Puurunen & Van Ommen, ALD 2020 online conference 29.6.-1.7.2020, pre-recorded poster talk (18.6.2020)
What is an ALD (temp...
Puurunen & Van Ommen, ALD 2020 online conference 29.6.-1.7.2020, pre-recorded poster talk (18.6.2020)
Growth/cycles
Proces...
Puurunen & Van Ommen, ALD 2020 online conference 29.6.-1.7.2020, pre-recorded poster talk (18.6.2020)
Equilibrium vs. accu...
Puurunen & Van Ommen, ALD 2020 online conference 29.6.-1.7.2020, pre-recorded poster talk (18.6.2020)
Growth per cycle (GP...
Puurunen & Van Ommen, ALD 2020 online conference 29.6.-1.7.2020, pre-recorded poster talk (18.6.2020)
Conclusion: The impo...
Puurunen & Van Ommen, ALD 2020 online conference 29.6.-1.7.2020, pre-recorded poster talk (18.6.2020)
Acknowledgements
• A...
Puurunen & Van Ommen, ALD 2020 online conference 29.6.-1.7.2020, pre-recorded poster talk (18.6.2020)
Title: On the fundam...
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"On the fundamentals of ALD: the importance of getting the picture right" by Puurunen and van Ommen Slide 1 "On the fundamentals of ALD: the importance of getting the picture right" by Puurunen and van Ommen Slide 2 "On the fundamentals of ALD: the importance of getting the picture right" by Puurunen and van Ommen Slide 3 "On the fundamentals of ALD: the importance of getting the picture right" by Puurunen and van Ommen Slide 4 "On the fundamentals of ALD: the importance of getting the picture right" by Puurunen and van Ommen Slide 5 "On the fundamentals of ALD: the importance of getting the picture right" by Puurunen and van Ommen Slide 6 "On the fundamentals of ALD: the importance of getting the picture right" by Puurunen and van Ommen Slide 7 "On the fundamentals of ALD: the importance of getting the picture right" by Puurunen and van Ommen Slide 8 "On the fundamentals of ALD: the importance of getting the picture right" by Puurunen and van Ommen Slide 9 "On the fundamentals of ALD: the importance of getting the picture right" by Puurunen and van Ommen Slide 10 "On the fundamentals of ALD: the importance of getting the picture right" by Puurunen and van Ommen Slide 11 "On the fundamentals of ALD: the importance of getting the picture right" by Puurunen and van Ommen Slide 12 "On the fundamentals of ALD: the importance of getting the picture right" by Puurunen and van Ommen Slide 13 "On the fundamentals of ALD: the importance of getting the picture right" by Puurunen and van Ommen Slide 14 "On the fundamentals of ALD: the importance of getting the picture right" by Puurunen and van Ommen Slide 15 "On the fundamentals of ALD: the importance of getting the picture right" by Puurunen and van Ommen Slide 16
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Presentation at the AVS 20th International Conference on Atomic Layer Deposition (ALD 2020) featuring the 7th International Atomic Layer Etching Workshop (ALE 2020), online, 29.6.-1.7.2020.

Authors: Riikka L. Puurunen and J. Ruud van Ommen

Abstract text:

Atomic layer deposition (ALD) has become of global importance as a fundamental building block for example in semiconductor device fabrication, and also gained more visibility (e.g., the Millennium Technology Prize 2018). In recent years, the number of ALD processes has increased, new groups have entered the field, and fundamental insights have been gained. At the same time, significantly varying views exist in the field related to the description and meaningfulness of some core ALD concepts. Open, respectful but critical scientific discussion would be needed around these concepts - for example at this AVS ALD/ALE conference, the world’s largest conference on ALD.

The discussion on terminology of ALD that started in the 2005 surface chemistry review [1] is continued in this contribution, taking into account recent progress reported in leading reviews such as Ref. 2. We start by considering the concept of “ideal ALD”. How should it be defined so that the well-recognized practical benefits of ALD are maintained, while no unnecessary utopian requirements are created? We propose that the repetition of well-separated saturating, irreversible chemisorption reactions (which by definition saturate at a monolayer of the chemisorbed species) is sufficient to reproduce the benefits of ALD. A requirement of “full monolayer growth” (of the ALD-grown material), progressed e.g. in numerous cartoons of ALD, is not needed. There should also be no reason to expect a constant growth per cycle (GPC) within the ALD window (the saturating chemistry is typically weakly temperature dependent), although such a scheme is repeatedly reproduced in the literature.

Other fundamental concepts will be pointed out, where mix-ups have been created. For example, although the GPC (or etch per cycle in Atomic Layer Etching) is a saturation-related concept and not a time-related kinetic parameter, Arrhenius plots have been sometimes created to extract “activation energies” of some process from these “growth/etch rates (per cycle)”. Also, “Langmuir adsorption” has been adopted as a way to model ALD in a simplified, lumped way. Notably, Langmuir adsorption assumes no interaction between adsorbed species, contrasting some recent discussions of “cooperative effects” in ALD. Also, concepts of “adsorption isotherm” and amount adsorbed vs. time (“saturation curve”), although fundamentally different, have been mixed.

We hope that the discussion on the fundamentals of ALD will be intensified, and that the discussion will help the field progress and flourish in the future.

[1] Puurunen, J. Appl. Phys. 97 (2005) 121301.
[2] Richey, de Paula, Bent, J. Chem. Phys. 152 (2020) 040902.

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"On the fundamentals of ALD: the importance of getting the picture right" by Puurunen and van Ommen

  1. 1. Puurunen & Van Ommen, ALD 2020 online conference 29.6.-1.7.2020, pre-recorded poster talk (18.6.2020) Riikka L. Puurunena J. Ruud van Ommenb aAalto University School of Chemical Engineering; bDelft University of Technology On the fundamentals of ALD: The importance of getting the picture right ALD 2020 online conference 29.6.-1.7.2020 Goulas, Puurunen, van Ommen 2020
  2. 2. Puurunen & Van Ommen, ALD 2020 online conference 29.6.-1.7.2020, pre-recorded poster talk (18.6.2020) 2 EuroCVD 22 - Baltic ALD 16, in Luxembourg, June 24-28, 2019. Virtual Project on the History of ALD (VPHA). Abstract Poster 2018 Millennium Technology Prize Dr. Tuomo Suntola 1974 Suntola Atomic Layer Epitaxy (ALE) http://vph-ald.com aldhistory.blogspot.fi 1965 1st record of Molecular Layering (ML) 1990 name Atomic Layer Deposition (ALD) introduced (?) 2007 Intel announces ALD high-k logic chips 1985 ALE-EL display production 2013 Virtual Project on the History of ALD launched 2001 first AVS ALD conference
  3. 3. Puurunen & Van Ommen, ALD 2020 online conference 29.6.-1.7.2020, pre-recorded poster talk (18.6.2020) Critical discussion on ALD fundamentals … Puurunen, Journal of Applied Physics 97 (2005) 121301; https://doi.org/10.1063/1.1940727 II.B Early experiments (ALE, ML)  II.C ALD processes  Citation to the J. Appl. Phys. 2005 review added in a recent erratum on a review article on the history of ALD: “Erratum: “History of atomic layer deposition and its relationship with the American Vacuum Society” [J. Vac. Sci. Technol. A 31, 050818 (2013)]” Journal of Vacuum Science & Technology A 38, 037001 (2020); https://doi.org/10.1116/6.0000143 Richey, de Paula, Bent, Understanding chemical and physical mechanisms in atomic layer deposition, Journal of Chemical Physics 152 (2020) 040902; https://doi.org/10.1063/1.5133390 Sønsteby, Yanguas-Gil, Elam, Consistency and reproducibility in atomic layer deposition, Journal of Vacuum Science & Technology A 38 (2020) 020804; https://doi.org/10.1116/1.5140603 https://www.atomiclimits.com/ald database/   3
  4. 4. Puurunen & Van Ommen, ALD 2020 online conference 29.6.-1.7.2020, pre-recorded poster talk (18.6.2020) Outline • Introduction: ALD growth & fundamental discussion • ALD cartoons over the years • What is ideal ALD? • ALD (temperature) window? • Adsorption isotherm vs. saturation with time • Growth per cycle (GPC) is not a rate • Conclusion 4
  5. 5. Puurunen & Van Ommen, ALD 2020 online conference 29.6.-1.7.2020, pre-recorded poster talk (18.6.2020) ALD cartoons over the years https://openlearning.aalto.fi/mod/page/view.php?id=7632; ALD-cartoons-evolving-file Koltsov, 1971 Suntola et al., 1980 Puurunen, 2005 Parsons et al., 2011 Leskelä & Ritala, 1995 George, 2010 Wikipedia, 2014 Knoops et al., 2015 5
  6. 6. Puurunen & Van Ommen, ALD 2020 online conference 29.6.-1.7.2020, pre-recorded poster talk (18.6.2020) Ideal ALD – one monolayer per cycle? https://commons.wikimedia.org/wiki/Category:Tuomo_Suntol a#/media/File:Reconstruction_of_the_first_atomic_layer_epit axy_experiment_by_Tuomo_Suntola.jpg 6 Puurunen, Chem. Vap. Dep. 20 (2014) 332; https://doi.org/10.1002/cvde.201402012
  7. 7. Puurunen & Van Ommen, ALD 2020 online conference 29.6.-1.7.2020, pre-recorded poster talk (18.6.2020) https://en.wikipedia.org/wiki/Atomic_layer_dep osition#/media/File:ALD_schematics.jpg “Full monolayer growth”, progressed e.g. in numerous cartoons of ALD, is an exception. Ideal ALD – one monolayer per cycle? 7 Puurunen, Chem. Vap. Dep. 20 (2014) 332; https://doi.org/10.1002/cvde.201402012
  8. 8. Puurunen & Van Ommen, ALD 2020 online conference 29.6.-1.7.2020, pre-recorded poster talk (18.6.2020) https://en.wikipedia.org/wiki/Atomic_layer_dep osition#/media/File:ALD_schematics.jpg “Full monolayer growth”, progressed e.g. in numerous cartoons of ALD, is an exception. Ideal ALD – one monolayer per cycle? 8 Puurunen, Chem. Vap. Dep. 20 (2014) 332; https://doi.org/10.1002/cvde.201402012
  9. 9. Puurunen & Van Ommen, ALD 2020 online conference 29.6.-1.7.2020, pre-recorded poster talk (18.6.2020) Ideal ALD - saturating reactions sufficient? Adapted from: Puurunen, J. Appl. Phys. 97 (2005) 121301; https://doi.org/10.1063/1.1940727 Saturating, irreversible reaction (chemisorption) Fully reversible (chemisorption or physisorption) Saturating, irreversible reaction, not saturated Combination of (1) saturating, irreversible reaction and (2) reversible physisorption Partly reversible chemisorption “ideal ALD” Not saturating (continuous CVD) amount time pulse purge 9
  10. 10. Puurunen & Van Ommen, ALD 2020 online conference 29.6.-1.7.2020, pre-recorded poster talk (18.6.2020) What is an ALD (temperature) window? Growth/cycles Process temperature ALD window L1 L2 H1 H2 See also: Sønsteby, Yanguas-Gil, Elam, JVSTA 38 (2020) 020804; https://doi.org/10.1116/1.5140603 10
  11. 11. Puurunen & Van Ommen, ALD 2020 online conference 29.6.-1.7.2020, pre-recorded poster talk (18.6.2020) Growth/cycles Process temperature ALD window L1 L2 H1 H2 GPC Temperature Temperature GPC What is an ALD (temperature) window? 11 Adapted from: Suntola, ”Atomic Layer Epitaxy”, Mater. Sci. Reports 4 (1989) 261-362; https://doi.org/10.1016/S0920-2307(89)80006-4 Puurunen, J. Appl. Phys. 97 (2005) 121301; https://doi.org/10.1063/1.1940727
  12. 12. Puurunen & Van Ommen, ALD 2020 online conference 29.6.-1.7.2020, pre-recorded poster talk (18.6.2020) Equilibrium vs. accumulation “… were fit using modified Langmuir adsorption isotherm expressions where the pressures are replaced with exposures.” J. Phys. Chem. A 114 (2010) 114; http://doi.org/10.1021/jp9049268 https://youtu.be/KddVM4nxgwIDerivation of the Langmuir adsorption isotherm - video 12
  13. 13. Puurunen & Van Ommen, ALD 2020 online conference 29.6.-1.7.2020, pre-recorded poster talk (18.6.2020) Growth per cycle (GPC) is not a (kinetic) reaction/growth rate http://aldhistory.blogspot.com/2016/10/term-growth-per-cycle-gpc-gaining-use.html, accessed 16.6.2020 https://en.wikipedia.org/wiki/Arrhenius_plot, accessed 16.6.2020 J. Appl. Phys. 97 (2005) 121301; https://doi.org/10. 1063/1.1940727 GPC ln(k) 1 / T Arrhenius equation & plot: 13
  14. 14. Puurunen & Van Ommen, ALD 2020 online conference 29.6.-1.7.2020, pre-recorded poster talk (18.6.2020) Conclusion: The importance of getting the picture right “Everything should be made as simple as possible, but not simpler” A. Einstein 14 Goulas, Puurunen, van Ommen 2020
  15. 15. Puurunen & Van Ommen, ALD 2020 online conference 29.6.-1.7.2020, pre-recorded poster talk (18.6.2020) Acknowledgements • Aris Goulas for patient improving of the ALD cartoon • Many people in the ALD community for critical discussion Riikka Puurunen • https://research.aalto.fi/en/persons/riikka- puurunen/ • Twitter: @rlpuu • https://www.slideshare.net/RiikkaPuurunen Ruud van Ommen • https://www.tudelft.nl/tnw/over- faculteit/afdelingen/chemical-engineering/principal- scientists/ruud-van-ommen/ • Twitter: @JRvanOmmen 15
  16. 16. Puurunen & Van Ommen, ALD 2020 online conference 29.6.-1.7.2020, pre-recorded poster talk (18.6.2020) 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 Abstract Text: Atomic layer deposition (ALD) has become of global importance as a fundamental building block for example in semiconductor device fabrication, and also gained more visibility (e.g., the Millennium Technology Prize 2018). In recent years, the number of ALD processes has increased, new groups have entered the field, and fundamental insights have been gained. At the same time, significantly varying views exist in the field related to the description and meaningfulness of some core ALD concepts. Open, respectful but critical scientific discussion would be needed around these concepts - for example at this AVS ALD/ALE conference, the world’s largest conference on ALD. The discussion on terminology of ALD that started in the 2005 surface chemistry review [1] is continued in this contribution, taking into account recent progress reported in leading reviews such as Ref. 2. We start by considering the concept of “ideal ALD”. How should it be defined so that the well- recognized practical benefits of ALD are maintained, while no unnecessary utopian requirements are created? We propose that the repetition of well- separated saturating, irreversible chemisorption reactions (which by definition saturate at a monolayer of the chemisorbed species) is sufficient to reproduce the benefits of ALD. A requirement of “full monolayer growth” (of the ALD-grown material), progressed e.g. in numerous cartoons of ALD, is not needed. There should also be no reason to expect a constant growth per cycle (GPC) within the ALD window (the saturating chemistry is typically weakly temperature dependent), although such a scheme is repeatedly reproduced in the literature. Other fundamental concepts will be pointed out, where mix-ups have been created. For example, although the GPC (or etch per cycle in Atomic Layer Etching) is a saturation-related concept and not a time-related kinetic parameter, Arrhenius plots have been sometimes created to extract “activation energies” of some process from these “growth/etch rates (per cycle)”. Also, “Langmuir adsorption” has been adopted as a way to model ALD in a simplified, lumped way. Notably, Langmuir adsorption assumes no interaction between adsorbed species, contrasting some recent discussions of “cooperative effects” in ALD. Also, concepts of “adsorption isotherm” and amount adsorbed vs. time (“saturation curve”), although fundamentally different, have been mixed. We hope that the discussion on the fundamentals of ALD will be intensified, and that the discussion will help the field progress and flourish in the future. [1] Puurunen, J. Appl. Phys. 97 (2005) 121301. [2] Richey, de Paula, Bent, J. Chem. Phys. 152 (2020) 040902. 16
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    Jun. 27, 2021

Presentation at the AVS 20th International Conference on Atomic Layer Deposition (ALD 2020) featuring the 7th International Atomic Layer Etching Workshop (ALE 2020), online, 29.6.-1.7.2020. Authors: Riikka L. Puurunen and J. Ruud van Ommen Abstract text: Atomic layer deposition (ALD) has become of global importance as a fundamental building block for example in semiconductor device fabrication, and also gained more visibility (e.g., the Millennium Technology Prize 2018). In recent years, the number of ALD processes has increased, new groups have entered the field, and fundamental insights have been gained. At the same time, significantly varying views exist in the field related to the description and meaningfulness of some core ALD concepts. Open, respectful but critical scientific discussion would be needed around these concepts - for example at this AVS ALD/ALE conference, the world’s largest conference on ALD. The discussion on terminology of ALD that started in the 2005 surface chemistry review [1] is continued in this contribution, taking into account recent progress reported in leading reviews such as Ref. 2. We start by considering the concept of “ideal ALD”. How should it be defined so that the well-recognized practical benefits of ALD are maintained, while no unnecessary utopian requirements are created? We propose that the repetition of well-separated saturating, irreversible chemisorption reactions (which by definition saturate at a monolayer of the chemisorbed species) is sufficient to reproduce the benefits of ALD. A requirement of “full monolayer growth” (of the ALD-grown material), progressed e.g. in numerous cartoons of ALD, is not needed. There should also be no reason to expect a constant growth per cycle (GPC) within the ALD window (the saturating chemistry is typically weakly temperature dependent), although such a scheme is repeatedly reproduced in the literature. Other fundamental concepts will be pointed out, where mix-ups have been created. For example, although the GPC (or etch per cycle in Atomic Layer Etching) is a saturation-related concept and not a time-related kinetic parameter, Arrhenius plots have been sometimes created to extract “activation energies” of some process from these “growth/etch rates (per cycle)”. Also, “Langmuir adsorption” has been adopted as a way to model ALD in a simplified, lumped way. Notably, Langmuir adsorption assumes no interaction between adsorbed species, contrasting some recent discussions of “cooperative effects” in ALD. Also, concepts of “adsorption isotherm” and amount adsorbed vs. time (“saturation curve”), although fundamentally different, have been mixed. We hope that the discussion on the fundamentals of ALD will be intensified, and that the discussion will help the field progress and flourish in the future. [1] Puurunen, J. Appl. Phys. 97 (2005) 121301. [2] Richey, de Paula, Bent, J. Chem. Phys. 152 (2020) 040902.

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