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EuroCVD-16-2007_Puurunen

Slides of an invited talk, given at EuroCVD in 2007

R. L. Puurunen, Understanding the surface chemistry of atomic layer deposition: achievements and challenges, Sixteenth European Conference on Chemical Vapor Deposition, EuroCVD-16. Den Haag, The Netherlands, 16 - 21 Sept. 2007. Book of Extended Abstracts. Klein, C.R. (Ed.). Delft University of Technology (2007), 11. Invited talk.

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EuroCVD-16-2007_Puurunen

  1. 1. Understanding the surface chemistry of ALD: Achievements and challenges Riikka Puurunen VTT Technology Development Centre of Finland
  2. 2. Riikka Puurunen, EuroCVD-16, 17 Sept 2007 2 • “The overall mechanism of deposition is extremely easy to understand. Surface O-H groups react with TMA … This leaves a methylated Al atom behind, free to react with H2O during the next vapor pulse …” • “A detailed understanding of growth process, however, requires that one explain the anomalously low growth rate … 1.1 Å … approximately half of a monolayer of Al2O3 ... This result is not understood at the present time.” Higashi & Fleming, 1989 Growth of Al2O3 by the AlMe3/H2O ALD process Appl. Phys. Lett. 55 (1989) 1963-1965. Al MeMe Me H2O Al2O3
  3. 3. Riikka Puurunen, EuroCVD-16, 17 Sept 2007 3 Outline 1. Introduction definition of ALD, ALD vs. CVD, growth per cycle, growth mode 2. Achievements: the AlMe3/H2O ALD process growth per cycle in the constant growth regime in the light of reaction mechanism studies 3. Challenges six open questions on the surface chemistry of ALD 4. Conclusion
  4. 4. Riikka Puurunen, EuroCVD-16, 17 Sept 2007 4 Outline 1. Introduction definition of ALD, ALD vs. CVD, growth per cycle, growth mode 2. Achievements: the AlMe3/H2O ALD process growth per cycle in the constant growth regime in the light of reaction mechanism studies 3. Challenges six open questions on the surface chemistry of ALD 4. Conclusion
  5. 5. Riikka Puurunen, EuroCVD-16, 17 Sept 2007 5 ALD cycles “Definition of ALD” “A film deposition technique that is based on the sequential use of self-terminating gas−solid reactions” Puurunen, 2005, J. Appl. Phys. ALD cycle Substrate before ALD Step 2 /4 Step 4 /4 Step 1 /4 Step 3 /4 purge purge Mass deposited
  6. 6. Riikka Puurunen, EuroCVD-16, 17 Sept 2007 6 ALD vs. the general scheme of CVD • ALD, additional requirement: self-terminating reactions x in ALD no gas phase reactions allowed separate pulsing of precursor vapors General CVD: saturating irreversible pulse purge
  7. 7. Riikka Puurunen, EuroCVD-16, 17 Sept 2007 7 Growth per cycle in ALD • GPC almost always < monolayer as function of temperatureas function cycle number ALD cycles GPC ALD cycles GPC ALD cycles GPC ALD cycles GPC Temperature GPC Temperature GPC Temperature GPC Temperature GPC Type I Type II
  8. 8. Riikka Puurunen, EuroCVD-16, 17 Sept 2007 8 Different growth modes in ALD • layer-by-layer growth (a) • island growth (b) • random growth (c) • island + layer-by-layer • layer-by-layer + island • … BeslingBesling et al., J. Nonet al., J. Non--CrystCryst. Solids 303 (2002) 123. Solids 303 (2002) 123--133133 (InAs)1 – (GaAs)5 superlattice UsuiUsui, Proc. IEEE, 80 (1992) 1641, Proc. IEEE, 80 (1992) 1641 on H-terminated Si
  9. 9. Riikka Puurunen, EuroCVD-16, 17 Sept 2007 9 Outline 1. Introduction definition of ALD, ALD vs. CVD, growth per cycle, growth mode 2. Achievements: the AlMe3/H2O ALD process growth per cycle in the constant growth regime in the light of reaction mechanism studies 3. Challenges six open questions on the surface chemistry of ALD 4. Conclusion
  10. 10. Riikka Puurunen, EuroCVD-16, 17 Sept 2007 10 AlMe3/H2O to Al2O3: growth per cycle vs. temperature • Al2O3 3.5 g cm-3 1 monolayer = 0.29 nm = 12.0 Al nm-2 0 0.05 0.1 0.15 0 100 200 300 Al2O3 ALD temperature (°C) Growthpercycle(nm) Ott1997a Matero2000 Putkonen2004 VTT, 2005 0 0.05 0.1 0.15 0 100 200 300 Al2O3 ALD temperature (°C) Growthpercycle(nm) Ott1997a Matero2000 Putkonen2004 VTT, 2005 VTT repeats saturatedunsaturated 0 1 2 3 4 5 6 0 100 200 300 Al2O3 ALD temperature (°C)Growthpercycle(Alnm -2 ) Ott1997a Matero2000 Puurunen2001a Jensen2002 Putkonen2004 Puurunen2004c VTT, 2005 all saturated
  11. 11. Riikka Puurunen, EuroCVD-16, 17 Sept 2007 11 Qualitative: reaction pathways, AlMe3 on oxides (data: IR, NMR, MS, QCM, element analysis, modelling) methane released all parts bonded CH4 ligand exchange reaction dissociation, association M OH Me3Al M O Me Me Al Me3Al M O M M O Me Me Al M Me M Me Me Al M Me O M O Me Al M O
  12. 12. Riikka Puurunen, EuroCVD-16, 17 Sept 2007 0 1 2 3 4 5 6 0 100 200 300 TMA reaction temp. (°C) Content(nm -2 ) Me Al 12 Quantitative: AlMe3 on oxides with controlled OH concentration • Reaction temperature has no effect • Substrate heat-treatment temperature affects strongly 560°C alumina, 3.4 OH/nm2 0 2 4 6 8 10 0 500 1000 Heat treatment (°C) Content(nm -2 ) OH Al 0 2 4 6 8 10 0 500 1000 Heat treatment (°C) Content(nm -2 ) OH Al alumina silica Puurunen, J. Appl. Phys. 97 (2005) 121301, and the refs. therein
  13. 13. Riikka Puurunen, EuroCVD-16, 17 Sept 2007 0 2 4 6 8 0 2 4 6 8 10 OH concentration (nm -2 ) Meadsorbed(nm -2 ) 13 Quantitative: AlMe3 on oxides with controlled OH concentration • 5-6 Me nm-2, non-ordered rather tightly packed y = 0.37x + 1.68 R 2 = 0.97 0 2 4 6 0 2 4 6 8 10 OH concentration (nm -2 ) Aladsorbed(nm -2 ) theor. max 7.2 nm-2 5.0 nm-2
  14. 14. Riikka Puurunen, EuroCVD-16, 17 Sept 2007 14 Quantitative: [Al] vs. [OH] mass balance: [Me] = 3 x [Al] - ∆[OH] 3 ]Me[ ]OH[ 3 1 ]Al[ +∆=⇒ experiment: [Al] = 0.37 [OH] + 1.68 Agreement with (1) complete reaction with OH’s (2) additionally dissociation/association (3) until reaction stops by steric hindrance 5-6 nm-2 y = 0.37x + 1.68 R 2 = 0.97 0 2 4 6 0 2 4 6 8 10 OH concentration (nm -2 ) Aladsorbed(nm -2 )
  15. 15. Riikka Puurunen, EuroCVD-16, 17 Sept 2007 15 AlMe3/H2O to Al2O3: growth per cycle vs. temperature • trend & absolute values explained, first time for ALD (?) • published in 2005, not once cited not noticed / disagreed on / regarded insignificant??? Puurunen, Appl. Surf. Sci. 245 (2005) 6 0 1 2 3 4 5 6 0 100 200 300 Al2O3 ALD temperature (°C) Growthpercycle(Alnm -2 ) Ott1997a Matero2000 Puurunen2001a Jensen2002 Putkonen2004 Puurunen2004c VTT, 2005 [Al] = 1.68 + 0.37[OH]
  16. 16. Riikka Puurunen, EuroCVD-16, 17 Sept 2007 16 Outline 1. Introduction definition of ALD, ALD vs. CVD, growth per cycle, growth mode 2. Achievements: the AlMe3/H2O ALD process growth per cycle in the constant growth regime in the light of reaction mechanism studies 3. Challenges six open questions on the surface chemistry of ALD 4. Conclusion
  17. 17. Riikka Puurunen, EuroCVD-16, 17 Sept 2007 (a) Which surface sites react with a given reactant? 17 Challenge 1. Qualitative understanding of the reactions OH O NH2 N (b) Surface species after the reaction? OH almost always assumed, are there others? SH S HNH etc L L M L L L M L L L LL LM L M etc
  18. 18. Riikka Puurunen, EuroCVD-16, 17 Sept 2007 (a) What is the real value of the GPC at different temperatures? Data by different groups (b) How is the GPC related to the no. of reactive sites on the surface Experiments on controlled substrates Temperature GPC 18 Challenge 2. Quantitative understanding of the reactions Temperature HfO2 GPC ? Temperature Al2O3 GPC OH GPC Al2O3 GPC OH content
  19. 19. Riikka Puurunen, EuroCVD-16, 17 Sept 2007 19 Challenge 3. Kinetics of ALD reactions • Description of reaction rates - classical chemical kinetic reaction rate models? • ALD reactions regarded “fast”, and mostly, mass transport defines cycle times • Rapidity & (assumed) irreversibility make performing kinetic measurements difficult • Even relative data on the rates of parallel/succeeding reactions would be relevant e.g., AlMe3 ligand exchange vs. dissociation
  20. 20. Riikka Puurunen, EuroCVD-16, 17 Sept 2007 20 Challenge 4. Growth mode in ALD processes on given substrates • “Two-dimensional growth” almost never demonstrated although often assumed • Monolayer-sensitive techniques (e.g. LEIS) need to be employed for studying the first cycles & tens of cycles Puurunen et al., J. Appl. Phys. 96 (2004) 4878 ZrO2 ALD on H-terminated Si 0 0.5 1 0 50 100 ALD cycles Surfacefraction 2-d RD LEIS ZrO2 surface fraction
  21. 21. Riikka Puurunen, EuroCVD-16, 17 Sept 2007 21 Challenge 5. Demonstrating quantitative relationship between computational chemistry and experiments • lots of ALD computational chemistry studies have been contributed to qualitative understanding • before computational chemistry can forecast the future, it must be able to reproduce the present 0 2 4 6 0 100 200 300 ALD temperature (°C) GPC(Alnm -2 ) Al2O3 GPC (Al nm-2)
  22. 22. Riikka Puurunen, EuroCVD-16, 17 Sept 2007 22 Challenge 6. Calculating the sizes of complex ligands • many simple models can assist in interpretations of ALD growth data • info needed: ligand sizes Model II Chemisorbed MLz M L MLn Model III Ligand L L Model I Reactant MLn Puurunen, J. Appl. Phys. 97 (2005) 121301 ( a review) N N M O M M O M O O M O M O O M M O NO M O M M M M M MM M M MM Organometallic M M Si M Metalorganic O M O N M O H O M O F FF F F F O M O O M O N M N M N M N M N Si M Si M N N O H O S N S M O M O O O N NM N NM
  23. 23. Riikka Puurunen, EuroCVD-16, 17 Sept 2007 23 Outline 1. Introduction definition of ALD, ALD vs. CVD, growth per cycle, growth mode 2. Achievements: the AlMe3/H2O ALD process growth per cycle in the constant growth regime in the light of reaction mechanism studies 3. Challenges six open questions on the surface chemistry of ALD 4. Conclusion
  24. 24. Riikka Puurunen, EuroCVD-16, 17 Sept 2007 24 Conclusion • Higashi, Fleming (1989) questions on the surface chemistry of AlMe3/H2O process to deposit Al2O3: now answered • With current techniques, we should be able to answer many similar questions -- are we still asking the questions? My wish list: • The 6-point list of open questions helps one to ask the relevant questions and to find answers • Ligand sizes calculated & published within 1-3 years?
  25. 25. Riikka Puurunen, EuroCVD-16, 17 Sept 2007 25 Acknowledgements • VTT Technical Research Center of Finland • Tekes Finnish Funding Agency for Technology and Innovation • Picosun • IMEC • TKK Helsinki University of Technology • Fortum Oil & Gas (Neste Oil) • ASM Microchemistry

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  • doolee00

    Jun. 13, 2015

Slides of an invited talk, given at EuroCVD in 2007 R. L. Puurunen, Understanding the surface chemistry of atomic layer deposition: achievements and challenges, Sixteenth European Conference on Chemical Vapor Deposition, EuroCVD-16. Den Haag, The Netherlands, 16 - 21 Sept. 2007. Book of Extended Abstracts. Klein, C.R. (Ed.). Delft University of Technology (2007), 11. Invited talk.

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