The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
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Deposition of Binary and Ternary Oxide Thin Films of Trivalent Metals by Atomic Layer Epitaxy

Minna Nieminen

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Chemical Technology for public examination and debate in Auditorium KE 2 (Komppa Auditorium) at Helsinki University of Technology (Espoo, Finland) on the 7th of December, 2001, at 12 noon.

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Abstract

The atomic layer epitaxy (ALE) technique was used to grow thin films of binary metal oxides Al2O3, Ga2O3 and La2O3, and ternary metal oxides LaNiO3, LaCoO3, LaAlO3, and LaGaO3. In addition, another type of mixed-oxide, viz. phosphorus-doped Al2O3 was studied. The binary oxides Ga2O3 and La2O3 and all the ternary oxides were deposited by the ALE method for the first time. New ALE processes were developed for the undoped and doped Al2O3 films. The thin films were characterized by a wide range of methods for structural and surface analysis, including XRD, FTIR, XPS, AFM, XRF, RBS, TOF-ERDA, and SIMS. A review of previous work on these trivalent metal oxide thin films is presented by way of background.

The Al2O3 and Ga2O3 films deposited from metal beta-diketonates and ozone were of high quality: stoichiometric, uniform, dense, and free of any significant contamination. However, the La2O3 films contained an excess of oxygen, due to the carbonate-type impurity that was detected. All Al2O3 and Ga2O3 films were amorphous, but polycrystalline, cubic La2O3 was formed at temperatures above 300 °C. Hexagonal La2O3 film was obtained by annealing the as-deposited amorphous and cubic La2O3 films. Simultaneously, the carbon content in the films was reduced. In contrast to the stable Al2O3 and Ga2O3 films, the cubic and hexagonal La2O3 films were chemically unstable and reacted with ambient air, transforming to LaO(OH) and La(OH)3, respectively.

The perovskite-type oxides LaNiO3, LaCoO3, LaAlO3, and LaGaO3 were deposited using metal beta-diketonates and ozone as precursors. No optimal ALE process could be demonstrated for the LaNiO3 and LaCoO3 films, which were non-uniform in thickness and either consisted of separate oxide layers or contained an excess of the transition metal. The LaAlO3 and LaGaO3 film growth, in contrast, was well-controlled yielding stoichiometric, uniform, and smooth films, demonstrating the potential of the ALE technique for producing the more complex ternary oxide films.

All the as-deposited ternary oxide films were amorphous but crystallized with cubic structure when post-annealed ex situ. After annealing high-quality, epitaxial LaAlO3 and LaGaO3 films were obtained on lattice-matched perovskite-type substrates while randomly or slightly oriented films were obtained on non-lattice matched substrates. The films were relatively pure and only small amounts of common impurities, carbon and hydrogen, were detected.

Phosphorus-doped Al2O3 films were deposited from AlCl3, P2O5 or trimethylphosphate, and water. The phosphorus content could be controlled by the phosphorus doping ratio: when the P/Al atomic ratio was below 1.0, the films consisted of both Al2O3 and AlPO4, whereas above that they contained predominantly AlPO4. Phosphorus was uniformly distributed when the phosphorus content exceeded 5 at.%, and it was enriched on the film/substrate interface when the content was lower.

This thesis consists of an overview and of the following 7 publications:

  1. Nieminen, M., Niinistö, L., and Lappalainen, R., Determination of P/Al ratio in phosphorus-doped aluminium oxide thin films by XRF, RBS and FTIR, Mikrochim. Acta 119 (1995) 13-22.
  2. Nieminen, M., Niinistö, L., and Rauhala, E., Growth of gallium oxide thin films from gallium acetylacetonate by atomic layer epitaxy, J. Mater. Chem. 6 (1996) 27-31.
  3. Nieminen, M., Putkonen, M., and Niinistö, L., Formation and stability of La2O3 thin films deposited from β-diketonate precursor, Appl. Surf. Sci. 174 (2001) 155-165.
  4. Seim, H., Mölsä, H., Nieminen, M., Fjellvåg, H., and Niinistö, L., Deposition of LaNiO3 thin films in an atomic layer epitaxy reactor, J. Mater. Chem. 7 (1997) 449-455.
  5. Seim, H., Nieminen, M., Niinistö, L., Fjellvåg, H., and Johansson, L.-S., Growth of LaCoO3 thin films from β-diketonate precursors, Appl. Surf. Sci. 112 (1997) 243-250.
  6. Nieminen, M., Sajavaara, T., Rauhala, E., Putkonen, M., and Niinistö, L., Surface-controlled growth of LaAlO3 thin films by atomic layer epitaxy, J. Mater. Chem. 11 (2001) 2340-2345.
  7. Nieminen, M., Lehto, S., and Niinistö, L., Atomic layer epitaxy growth of LaGaO3 thin films, J. Mater. Chem. (2001), in press.

Keywords: atomic layer epitaxy, atomic layer deposition, thin films, ternary oxides, binary oxides

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© 2002 Helsinki University of Technology


Last update 2011-05-26