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.
Aalto

Atomic Layer Deposition of High-k Dielectrics from Novel Cyclopentadienyl-Type Precursors

Jaakko Niinistö

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 TU1 at Helsinki University of Technology (Espoo, Finland) on the 12th of May, 2006, at 12 noon.

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Dissertation is also available in print (ISBN 951-22-8169-4)

Abstract

The atomic layer deposition (ALD) method was applied for fabricating high permittivity (high-k) dielectrics, viz. HfO2, ZrO2 and rare earth oxides, which can be used to replace SiO2 as gate and capacitor dielectric. The dielectrics were processed by ALD using novel cyclopentadienyl (Cp, -C5H5) precursors together with water or ozone as the oxygen source. ALD, which has been identified as an important thin film growth technique for microelectronics manufacturing, relies on sequential and saturating surface reactions of alternately applied precursors, separated by inert gas purging. The surface-controlled nature of ALD enables the growth of thin films of high conformality and uniformity with an accurate thickness control.

The ALD technique is introduced and ALD processes for HfO2, ZrO2 and rare earth oxide films, as well as the applications of the high-k dielectrics in microelectronics are reviewed. The need for developing new ALD processes for the high-k materials is emphasized.

ALD processes for HfO2 and ZrO2 were developed using Cp-type precursors. The effect of different oxygen sources, namely water or ozone, on the film growth characteristics and properties of the ALD-processed films was examined in detail. The oxide films were stoichiometric, with impurity levels below even 0.1 at-% for C or H. Electrical measurements showed promising dielectric properties such as high permittivity values and low leakage current densities. Other properties, such as structure, interfacial layer thickness and morphology, were also characterized. Compared to films processed by water, the ozone-processed films on H-terminated Si showed improved dielectric properties, as well as higher density, lower roughness and better initial growth rate. In addition, in situ gas-phase measurements by quadrupole mass spectrometry (QMS) were performed in order to study the ZrO2 growth mechanism.

A number of Cp-precursors were tested for the ALD of several rare earth oxide films. The thermal stability of many of the precursors was limited, but nevertheless, ALD-type processes were developed for Y2O3 and Er2O3 films. High reactivity of the Cp-precursors towards water resulting in high growth rates (1.2-1.7 Å/cycle) and purity of the Y2O3 and Er2O3 films were realized. Despite the detected partial decomposition of the (CpMe)3Gd precursor, Gd2O3 films with high growth rate and purity as well as effective permittivity of about 14 were deposited.

Finally, promising processes for ternary scandates, namely YScO3, GdScO3, and ErScO3, were developed using either Cp- or β-diketonate-based processes. These as-deposited ternary films were amorphous exhibiting high effective permittivity (14-15), low leakage current density, and resistance towards crystallization upon annealing even up to 800°C.

This thesis consists of an overview and of the following 9 publications:

  1. Putkonen, M., Niinistö, J., Kukli, K., Sajavaara, T., Karppinen, M., Yamauchi, H., and Niinistö, L., ZrO2 thin films grown on silicon substrates by atomic layer deposition with Cp2Zr(CH3)2 and water as precursors, Chemical Vapor Deposition 9 (2003) 207-212.
  2. Niinistö, J., Putkonen, M., Niinistö, L., Kukli, K., Ritala, M., and Leskelä, M., Structural and dielectric properties of thin ZrO2 films on silicon grown by atomic layer deposition from cyclopentadienyl precursor, Journal of Applied Physics 95 (2004) 84-91.
  3. Niinistö, J., Rahtu, A., Putkonen, M., Ritala, M., Leskelä, M., and Niinistö, L., In situ quadrupole mass spectrometry study of atomic-layer deposition of ZrO2 using Cp2Zr(CH3)2 and water, Langmuir 21 (2005) 7321-7325.
  4. Niinistö, J., Putkonen, M., Niinistö, L., Stoll, S. L., Kukli, K., Sajavaara, T., Ritala, M., and Leskelä, M., Controlled growth of HfO2 thin films by atomic layer deposition from cyclopentadienyl-type precursor and water, Journal of Materials Chemistry 15 (2005) 2271-2275.
  5. Niinistö, J., Putkonen, M., Niinistö, L., Arstila, K., Sajavaara, T., Lu, J., Kukli, K., Ritala, M., and Leskelä, M., HfO2 films grown by ALD using cyclopentadienyl-type precursors and H2O or O3 as oxygen source, Journal of The Electrochemical Society 153 (2006) F39-F45.
  6. Niinistö, J., Putkonen, M., and Niinistö, L., Processing of Y2O3 thin films by atomic layer deposition from cyclopentadienyl-type compounds and water as precursors, Chemistry of Materials 16 (2004) 2953-2958.
  7. Niinistö, J., Petrova, N., Putkonen, M., Sajavaara, T., Arstila, K., and Niinistö L., Gadolinium oxide thin films by atomic layer deposition, Journal of Crystal Growth 285 (2005) 191-200.
  8. Päiväsaari, J., Niinistö, J., Arstila, K., Kukli, K., Putkonen, M., and Niinistö, L., High growth rate of erbium oxide thin films in atomic layer deposition from (CpMe)3Er and water precursors, Chemical Vapor Deposition 11 (2005) 415-419.
  9. Myllymäki, P., Nieminen, M., Niinistö, J., Putkonen, M., Kukli, K., and Niinistö, L., High-permittivity YScO3 thin films by atomic layer deposition using two precursor approaches, Journal of Materials Chemistry 16 (2006) 563-567.

Keywords: atomic layer deposition, ALD, high-k dielectrics, oxide thin films, cyclopentadienyl

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© 2006 Helsinki University of Technology

Last update 2011-05-26