High-k ternary rare earth oxides by atomic layer deposition

Pia Myllymäki
Abstract & Cover

The present thesis describes atomic layer deposition (ALD) of ternary rare earth (RE) oxides and characterization of compositional, structural and electrical properties of the films. The REScO3, LaLuO3 and ErxGa2-xO3 thin films investigated are potential high-κ materials for future metal-oxide-semiconductor field-effect transistors, i.e. MOSFETs. The dissertation consists of five peer reviewed publications. As a background for the work, issues related to the miniaturization of MOSFETs and the feasibility of rare earth oxides as new high-κ dielectrics are discussed. Also some challenges of manufacturing Ga-based MOSFETs with high quality gate oxide having satisfactory interface properties and the role of rare earth oxides in GaAs passivation are presented. In addition the basic principle of the ALD method is briefly introduced and recent literature concerning deposition of rare earth oxides is reviewed. A series of REScO3 thin films was deposited by ALD using rare earth β-diketonate precursors RE(thd)3 together with ozone. The films were characterized for growth rate, elemental composition, crystallization upon annealing and electrical properties. Amorphous films of high quality with low impurity contents and promising electrical characteristics were produced. Several gradually evolving properties of the films were examined and the effect of the RE3+ cation size was discussed. YScO3 films were also deposited using novel cyclopentadienyl metal precursors and water. Deposition of LaLuO3 films having similar properties but even higher dielectric constant (κ ≈ 30) than ternary scandates was examined at two different temperatures. The relationship between the crystallization behaviour and the dielectric constant of REScO3 and LaLuO3 thin films was discussed. Finally deposition of a possible gate oxide for GaAs MOSFETs, viz. ErxGa2-xO3 by two different precursor approaches was investigated. In addition to β-diketonate metal precursors novel cyclopentadienyl and amidinate metal precursors together with water as oxygen source were utilized. For both YScO3 and ErxGa2-xO3 films the choice of precursor system affected e.g. the electrical properties and the crystallization behavior.

Source of Information
FinALD40 exhibition material, http://www.aldcoe.fi/events/finald40.pdf
Aalto University, School of Science and Technology, Faculty of Chemistry and Materials Sciences, Department of Chemistry, Laboratory of Inorganic Chemistry
(Espoo, Finland)
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