Oxide thin films by ALD for advanced applications

1
Oxide thin films by ALD for advanced applications

• Lauri Niinistö
• Helsinki University of Technology (HUT)
• Espoo, Finland
• Lauri.Niinisto_at_hut.fi

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Contents

• Milestones in the development of ALD
• 1.1 Methods and reactors
• 1.2 Materials and products
• 2. Oxide ALD
• 2.1 For TFEL displays
• 2.2 For other applications
• 3. Current technological change in semiconductor
  industry

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• 4. Deposition of high-k materials by ALD
• 4.1 Precursor chemistry
• 4.2 Some problems in precursor chemistry and
  how to solve them
• 4.3 Binary oxides
• 4.4 Pseudobinary and ternary oxides
• 5. Conclusions
• 6. Acknowledgements

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1. Milestones in the development of ALD

• Atomic Layer Deposition, originally referred to
  as Atomic Layer Epitaxy (ALE), was developed by
  Dr. T. Suntola and co-workers in Finland to meet
  the needs of producing improved thin films and
  structures based thereupon for electroluminescent
  thin film (TFEL) flat panel displays
• First Finnish Patent 1974
• First U.S. patent 1977
• Other patents

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1.1 Methods and Reactors

• First ALD reactor was a simple vacuum apparatus
  for deposition of ZnS from the elements

T. Suntola and J. Hyvärinen Ann. Rev. Mater. Sci.
15 (1985) 177.
6

• A succesful concept Travelling wave (gas
  flow-type) ALD reactor in 1978
• The self-controlling nature of an ALD process
  allows for an easy scaling-up of the reactor and
  substrate for large-area production purposes

Research-type F120 reactor from ASM
Microchemistry 1. N2-generator 2.
Oxidizer 3. Pulsing valves 4. Heaters 5. Precurso
r 6. Pulsing gas lines 7. Substrates 8. Exhaust
line
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1.2 Materials and products

• 1983 volume production of yellow-emitting thin
  film EL devices was begun at Lohja corporation
  (later Planar International)
• TFEL is a complex structure having
  insulator-semiconductor-insulator stack of thin
  films as its core
• 1993 first commercial multicolor (R/G/Y) TFEL
  panel
• Another early application Catalyst preparation
  by ALD

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2. Oxide ALD

• 2.1 For TFEL displays
• Oxide ALD was done since the 1980s in Finland by
  Lohja Corporation Electronics Division (later
  Planar International) on an industrial scale for
  dielectrics in the TFEL structures
• alumina from Al chloride and water
• ATO (Al-Ti-oxide)

A simplified view of an EL device
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2.2 For other applications

• Another application for oxide ALD is the
  deposition of tin dioxide for gas sensor
  applications
•   the inherent surface-controlled properties
  of an ALD process can be exploited to an
  extreme when pores with high aspect ratio
  (1401) in porous silicon (PS) can be
  conformally coated as shown by XTEM and SIMS
  studies

C. Ducsö and L. Niinistö et al. J. Electrochem.
Soc. 143 (1996) 683.
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• Objects of almost any size and shape can be
  coated. Example AFM tips

M. Utriainen et al. Appl. Phys. A 68 (1999) 339.
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3. Current technological change in semiconductor
industry

• Many materials are currently under consideration
  as potential candidates for gate dielectrics for
  sub 0.1 µm CMOS technology
• Silicon dioxide with an dielectric constant of
  3.9 will be replaced by so-called high-k
  materials
• Candidates for gate dielectrics include the
  oxides of yttrium, lanthanum, zirconium and
  hafnium, which have much higher dielectric
  constants than SiO2
• We have demonstrated that these dielectrics can
  be deposited in a controlled way by ALD

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Some high-k candidates
G. D. Wilk et al. J. Appl. Phys. 89 (2001) 5243.
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4. Deposition of high-k materials by ALD

• Because ALD is a chemical method it offers a wide
  range of
• alternatives (precursor combinations) for the
  deposition of
• metal oxides.
• 4.1 Precursor chemistry for metal oxide thin
  films
• Metal source
• - halides (a)
• - alkoxides (b)
• - ß-diketonate complexes (c)
• - organometallics (d) (e)
• Oxygen source O2, H2O, O3, H2O2, etc.

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• The volatility and thermal stability of a
  precursor can be conveniently checked by
  thermogravimetry under reduced pressure (ALD
  deposition conditions). For example,
  Zr-precursors

M. Putkonen and L. Niinistö, J. Mater. Chem. 11
(2001) 3141.
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4.2 Some problems in precursor chemistry and how
to solve them

• Rare earth and alkaline earth ions have large
  sizes (ionic radii) and are thus in many
  compounds coordinatively unsaturated. This easily
  leads to reactions with the ambient and to
  oligomerization which may reduce or destroy the
  volatility of the precursor in an ALD process.
• Two possible solutions to overcome the problem
• (1) adducting the precursor and this way
  saturating its coordination sphere and protecting
  the metal ion from reacting with the ambient

CN 6 2 8
CN 6 2 8
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• (2) in situ synthesis of the precursor providing
  a fresh and reactive supply of it
  onto the substrate

P.Soininen et al. Chem. Vap. Deposition 2 (1996)
69.
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• By properly choosing the precursor chemistry one
  can influence
• growth rate and temperature
• impurity levels of the films
• A recent
• example Sc2O3

M. Putkonen et al. Chem. Mater. 13 (2001) 4701.
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• Annealing may be used to crystallize the film
  and/or induce chemical or structural changes

M. Nieminen, M. Putkonen and L. Niinistö, Appl.
Surf. Sci. 174 (2001) 155.
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4.3 Binary oxides

• Early work in 1980s on oxides in our laboratory
  was focused on Al2O3 as insulator in the TFEL
  structure
• By exploiting precursor chemistry and
  organometallics other refractory oxides have been
  prepared as well

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Examples of binary oxides processed by ALD at HUT

• Group 2 MgO
• Group 3 Sc2O3 , Y2O3 , La2O3,, CeO2 , Gd2O3 ,
  Er2O3
• Group 4 TiO2 , ZrO2 , HfO2
• Group 5 V2O5
• Group 10 NiO
• Group 12 CuO
• Group 13 Al2O3 , Ga2O3
• Group 14 SnO2

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ALD growth rates of selected oxide thin films
the large and basic cations (Ba, Sr and La)
first react and form carbonates which by
annealing can be converted to oxides
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4.4 Pseudobinary and ternary oxides

• Most studies in our laboratory have been focused
  on YSZ (yttrium-stabilized zirconia) but other
  doped oxides have been studied as well, e.g.
  Al2O3P
• For the true ternary compounds, the perovskite
  oxides containing La have been processed by ALD,
  for instance LaAlO3 and LaGaO3

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M. Putkonen, Helsinki University of Technology,
Inorganic Chemistry Publication Series No.2
(2002) 1-69.
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• By a suitable selection of precursor pulsing
  ratios, stoichiometric LaAlO3 and LaGaO3 films
  could be obtained at deposition temperatures
  between 325 and 400C

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• The impurity levels in ternary oxide films were
  low, for instance LaGaO3 films processed from
  diketonate precursors contained only 0.4 and 0.2
  at- carbon and hydrogen, respectively as
  analysed by TOF-ERDA
• With matching substrates, epitaxial and smooth
  LaAlO3 and LaGaO3 thin films were obtained after
  annealing. This was verified by rocking curve and
  AFM measurements

M. Nieminen et al. J. Mater. Chem. 11 (2001) 2340
and 11 (2001) 3148.
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M. Nieminen et al. J. Mater. Chem. 11 (2001) 2340
and 11 (2001) 3148.
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5. Conclusions

• ALD processes including novel precursors have
  been developed for several metal oxides (e.g.
  ZrO2) which are potential candidates for high-k
  dielectrics
• By a suitable choice of the precursor chemistry,
  precursor stability and growth rate can be
  enhanced while the growth temperature and the
  impurity levels for the resulting films are
  lowered
• Also pseudobinary and ternary oxides can be
  deposited by combining two binary processes.
  Thus, epitaxial and smooth perovskite oxide
  films, for instance LaAlO3 and LaGaO3 have been
  grown

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Acknowledgements

• Helsinki University of Technology
• Hiltunen, Lassi
• Iiskola, Eero
• Johansson, Johanna
• Johansson, Leena-Sisko
• Karppinen, Maarit
• Keränen, Jetta
• Kosola, Anne
• Leskelä, Tuula
• Nieminen, Minna
  
• Niinistö, Jaakko
  
• Putkonen, Matti
• Päiväsaari, Jani
• and former ALD co-workers

• University of Helsinki
• Kukli, Kaupo
• Leskelä, Markku
• Rauhala, Eero
• Ritala, Mikko
• Sajavaara, Timo

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Acknowledgements (contnd)

• Visiting Scientists and Collaborating
• Partners
• Auroux, Aline (Villeurbanne, France)
• Bombicz, Petra (Budapest, Hungary)
• Fjellvåg, Helmer (Oslo, Norway)
• Friedbacher, Gernot (Vienna, Austria)
• Kareiva, Aivaras (Vilnius, Lithuania)
• Krunks, Malle (Tallinn, Estonia)
• Madarasz, Janos (Budapest, Hungary)
• Meszaros Szecsenyi, Katalin (Budapest, Hungary)
• Pokol, György (Budapest, Hungary)
• Sammelselg, Väino (Tartu, Estonia)
• Stoll, Sarah L. (Georgetown, Washington D.C, USA)

• Industrial partners
• ASM Microchemistry Ltd (Espoo, Finland)
• Planar International Ltd (Espoo, Finland)
• Vaisala Ltd (Vantaa, Finland)
• Environics Ltd (Mikkeli, Finland)

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Acknowledgements (contnd)

• Thanks are also due to ALD2002 conference
  organizers and the Foundation of Fortum Ltd for
  their generous support towards travel and
  attendance.

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Recent ALD publications (2000-2002) at the
Helsinki University of Technology. An annotated
list

• Reviews
• 1. Niinistö, L Advanced thin films for
  electronics and optoelectronics by atomic layer
  epitaxy, Proc. Int. Semicond. Conf. CAS 1 (2000)
  33-42. A review with 78 refs. covering the
  literature until 2000.
• 2. Nieminen, M. Deposition of binary and ternary
  oxide thin films of trivalent metals by atomic
  layer epitaxy, Helsinki University of Technology,
  Inorganic Chemistry Publication Series No.1
  (2001) 1-57. A review with 190 refs. and a
  discussion of authors own results on La, Al, and
  Ga.
• 3. Päiväsaari, J. and Niinistö, L., Growth of
  rare-earth oxide thin films for electronic
  applications by atomic layer deposition, ERES
  Newsletter 12 (2001) No.2 pp. 1-3. An
  introduction to the principles of ALD/ALE with
  examples from the authors recent work
• 4. Putkonen, M., Development of low-temperature
  deposition processes by atomic layer epitaxy for
  binary and ternary oxide thin films, Helsinki
  University of Technology, Inorganic Chemistry
  Publication Series No.2 (2002) 1-69. A review
  with 174 refs. and a discussion of authors own
  results on Sc, Zr, Mg, Y, La oxides as well as
  YSZ.

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Recent ALD publications (2000-2002) at the
Helsinki University of Technology

• Original articles
• 5. Putkonen, M., Sajavaara, T. and Niinistö, L.,
  Enhanced growth rate in atomic layer epitaxy
  deposition of magnesium oxide thin films, J.
  Mater. Chem. 10 (2000) 1857-1861.The use of
  cyclopentadienyl-type of true organometallics
  leads to relatively high growth rates at
  reasonable temperatures.
• 6. Nieminen, M. Putkonen, M. and Niinistö, L.,
  Formation and stability of La2O3 thin films
  deposited from beta-diketonate precursor, Appl.
  Surf. Sci. 174 (2001) 155-165. A detailed
  discussion of and experimental evidence for the
  formation of La oxide thin films.
• 7. Nieminen, N., Sajavaara, T.,, Rauhala, E.,
  Putkonen, M. ja Niinistö, L. Surface-controlled
  growth of LaAlO3 thin films by atomic layer
  epitaxy, J. Mater. Chem. 11 (2001) 2340-2345.
  Effect of substrates is demonstrated and in one
  case (hetero)epitaxial growth of LaAlO3 is
  achieved.
• 8. Utriainen, M., Kröger-Laukkanen, M.,
  Johansson, L-S. and Niinistö,L., Studies of
  metallic
• film growth in an atomic layer epitaxy reactor
  using M(acac)2 (MNi, Cu, Pt) precursors, Appl.
  Surf. Sci. 157 (2000) 151-158. Two strategies are
  described to deposit metals by ALD.
• 9. Utriainen, M., Lattu, H., Viirola, H.,
  Niinistö, L., Resch, R. and Friedbacher, G.,
  Atomic force microscopy studies of SnO2 thin film
  microstructures deposited by atomic layer
  epitaxy., Microchim. Acta 133 (2000) 119-133. Tin
  dioxide grows heteroepitaxially on sapphire.
• 10. Putkonen, M., Sajavaara, T.,Johansson, L.-S.,
  and Niinistö, L., Low-temperature ALE
  deposition of Y2O3 thin films
  from beta-diketonate precursors, Chem. Vap.
  Deposition 7 (2001) 44-50. thd-type substituted
  and non-substituted precursors are used to grow
  yttria thin films.

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Recent ALD publications (2000-2002) at the
Helsinki University of Technology

• 11. Kröger-Laukkanen, M., Peussa, M., Leskelä,
  M. and Niinistö, L., Reactions of
  
  
• bis(cyclopentadienyl)zirconium dichloride with
  porous silica surface, Appl. Surf. Sci.
• 183 (2001) 290-300. A study of the reaction
  mechanism when Zr precursor is adsorbed.
• 12. Keränen, J., Auroux, A., Ek-Härkönen, S.,
  and Niinistö, L., Calorimetric measurements of
  the acidity of
  supported vanadium oxides by ALE and
  inpregnation, Thermochim. Acta 379 (2001)
  233-239. A comparison of the acidity and activity
  of ALE/ALD oxides vs. impregnated ones.
• 13. Nieminen, M., Lehto, S. and Niinistö, L.,
  Atomic layer epitaxy growth of LaGaO3 thin films,
  J. Mater. Chem. 11 (2001) 3148-3153. Lanthanum
  gallate can be epitaxially grown onto La
  aluminate and Sr-titanate substrates.
• 14. Putkonen, M., Nieminen, M., Niinistö, J,,
  and Niinistö, L., Surface-controlled deposition
  of Sc2O3 thin films by atomic layer epitaxy
  using beta-diketonate and organometallic
  precursors, Chem. Mater. 13 (2001) 4701-4707.
  Three precursor combinations were used to deposit
  Sc- oxide, Sc-Cp H2O giving the highest growth
  rate.
•   15 . Iiskola, E. and Niinistö, L., The
  preparation of homogenous surfaces for catalysis
  gas-solid interactions of alkoxysilanes with
  high surface area silica, Silica 2001 Short
  abstracts, Mulhouse, France 2001, p. 84. (full
  paper on CD-ROM). Saturated gas-solid ALD-type
  reactions can be used to prepare catalyst
  support materials in a reproducible way.
• 16. Keränen, J., Ek, S., Iiskola, E., Auruoux,
  A., and Niinistö, L., Controlled formation of
  thin V2O5 layers on silica by atomic layer
  deposition, Silica 2001 Short abstracts,
  Mulhouse, France 2001, p. 90,(full paper on
  CD-ROM) Catalysts with improved properties can be
  prepared by ALD- dispersing of silica with
  vanadia.
•  

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Recent ALD publications (2000-2002) at the
Helsinki University of Technology

• 17. Putkonen, M. and Niinistö, L., Zirconia thin
  films by atomic layer epitaxy. A comparative
  study on the use of novel precursors with ozone,
  J. Mater. Chem. 12 (2001) 3141-3147. Cp-type true
  organometallics lead to higher growth rates and
  lower deposition temperatures than the
  conventional beta-diketonate precursors.
• 18. Johansson, J. Kostamo, J., Karppinen, M. and
  Niinistö, L., Growth of conductive copper sulfide
  thin films by atomic layer deposition, J. Mater.
  Chem. 12 (2002) 1022-1026.The films grown by ALD
  exhibit the best reported conductivity values.
• 19 Keränen, J., Auroux, A., Ek, S. and Niinistö,
  L., Preparation, characterization and activity
  testing of vanadia catalysts deposited onto
  silica and alumina supports by atomic layer
  deposition, Appl. Catalysis A. 228 (2002)
  213-225. The ALD-prepared catalysts showed
  improved activity over the vanadia-catalysts
  prepared by impregnation.
• 20. Meszaros-Szecsenyi, K., Päiväsaari, J.,
  Putkonen, M., Niinistö, L. and Pokol, G.,
  Scandium dipivaloyl methanate as a volatile
  precursor for thin film deposition. Coupling of
  mass spectrometer to thermobalance, J. Therm.
  Anal. Calorim. 69 (2002) 65-75. Sc(thd)3
  precursor was investigated for thin film
  depositions.
• 21. Putkonen, M., Sajavaara, T., Niinistö, J.,
  Johansson, L.-S., and Niinistö, L, Deposition of
  yttria-stabilized zirconia thin films by atomic
  layer epitaxy from beta-diketonate and
  organometallic precursors, J. Mater. Chem. 12
  (2002) 442-448. After developing ALD processes
  for the component oxides, the deposion of the
  ternary one was straightforward.
• 22. Päiväsaari, J., Putkonen, M. and Niinistö,
  L., Cerium dioxide buffer layers at low
  temperature by atomic layer deposition, J. Mater.
  Chem. 12 (2002) 1828-1832. The refractory cerium
  dioxide can be deposited even at 175 C using
  Ce(thd)4 and ozone as precursors.

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Recent ALD publications (2000-2002) at the
Helsinki University of Technology

• 23. Keränen,J., Iiskola, E., Guimon, C., Auroux,
  A. and Niinistö, L., Controlled coating of high
  surface area silica with titania overlayers by
  atomic layer deposition, to be published.
  ALD-coated silica has been characterized by XRD,
  DRIFTS, XPS, TEM and UV-vis DRS measurements.
• 24. Niinistö, L., Atomic layer deposition A key
  technology for the controlled growth of
• thin films for advanced applications.
  Proceedings of the 5th Baltic Symposium on
• Atomic Layer Deposition,Tartu, Estonia, 2002, to
  be published. A review on the principles and
  applications of ALD.