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Metal organic chemical vapor deposition of ultrathin ZrO2 films on Si(100) and Si(111) studied by electron spectroscopy
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
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2007 (English)In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 601, no 4, 1008-1018 p.Article in journal (Refereed) Published
Abstract [en]

The growth of ultrathin ZrO2 films on Si(1 0 0)-(2 × 1) and Si(1 1 1)-(7 × 7) has been studied with core level photoelectron spectroscopy and X-ray absorption spectroscopy. The films were deposited sequentially by chemical vapor deposition in ultra-high vacuum using zirconium tetra-tert-butoxide as precursor. Deposition of a > 50 Å thick film leads in both cases to tetragonal ZrO2 (t-ZrO2), whereas significant differences are found for thinner films. On Si(1 1 1)-(7 × 7) the local structure of t-ZrO2 is not observed until a film thickness of 51 Å is reached. On Si(1 0 0)-(2 × 1) the local geometric structure of t-ZrO2 is formed already at a film thickness of 11 Å. The higher tendency for the formation of t-ZrO2 on Si(1 0 0) is discussed in terms of Zr–O valence electron matching to the number of dangling bonds per surface Si atom. The Zr–O hybridization within the ZrO2 unit depends furthermore on the chemical composition of the surrounding. The precursor t-butoxy ligands undergo efficient C–O scission on Si(1 0 0), leaving carbonaceous fragments embedded in the interfacial layer. In contrast, after small deposits on Si(1 1 1) stable t-butoxy groups are found. These are consumed upon further deposition. Stable methyl and, possibly, also hydroxyl groups are found on both surfaces within a wide film thickness range.

Place, publisher, year, edition, pages
2007. Vol. 601, no 4, 1008-1018 p.
Keyword [en]
High dielectrics, Zirconium dioxide, Silicon, Chemical vapor deposition, Semiconductor–insulator interfaces, Synchrotron radiation photoelectron spectroscopy, X-ray absorption spectroscopy
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-94946DOI: 10.1016/j.susc.2006.11.038ISI: 000245155800020OAI: oai:DiVA.org:uu-94946DiVA: diva2:168978
Available from: 2006-10-13 Created: 2006-10-13 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Electronic Properties of Metal Oxide Films Studied by Core Level Spectroscopy
Open this publication in new window or tab >>Electronic Properties of Metal Oxide Films Studied by Core Level Spectroscopy
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this dissertation core level electron spectroscopy has been employed to study various aspects of metal oxide films grown under ultra-high vacuum conditions.

Studies on in situ ion insertion of lithium into thin TiO2 systems were performed. The electronic and geometric properties are investigated in detail, along with an estimation of charge transfer from Li to Ti.

A detailed study of chemical vapour deposition of ZrO2 on Si(100)-(2x1) was performed. ZrO2 is found to be an insulator, i.e. its electronic levels are decoupled from the substrate and the Zr levels are best referenced to the local vacuum level. The alignment of the valence and conduction band has been determined.

Combinatorial chemical vapour deposition of TiO2 and ZrO2 on Si(100)-(2x1) was realized. A film with graded stoichiometry consisting of pure TiO2 and ZrO2 on the opposing ends and mixed composition of both oxides in the middle was obtained. A detailed study of the electronic levels revealed that ZrO2 remains an insulator in the monolayer regime and that modification of ZrO2 with a small amount of TiO2 leads to a more symmetric alignment of the bands relative to Si.

The influence of a core hole on the O 1s x-ray absorption spectrum in TiO2 and ZrO2 is elucidated. Supported by O 1s photoemission measurements and ab initio calculations it is concluded that the static final state picture as well as dynamical threshold effects must be considered in order to determine the location of the conduction band minimum within the XAS framework.

Finally a Co modified Co:ZnO film was shown to display ferromagnetic properties. It could be evidenced that Co with oxygen as nearest neighbours was responsible for the magnetism and not metallic Co.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2006. 69 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 228
Keyword
Physics, electron spectroscopy, metal oxide, chemical vapour deposition, ion insertion, metal organic, band alignment, zirconium, titanium, silicon, high k, Fysik
Identifiers
urn:nbn:se:uu:diva-7180 (URN)91-554-6673-7 (ISBN)
Public defence
2006-11-03, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15
Opponent
Supervisors
Available from: 2006-10-13 Created: 2006-10-13 Last updated: 2011-02-10Bibliographically approved
2. Surface Science Studies of Metal Oxides Formed by Chemical Vapour Deposition on Silicon
Open this publication in new window or tab >>Surface Science Studies of Metal Oxides Formed by Chemical Vapour Deposition on Silicon
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

For an electronic device well-designed interfaces are critical for the performance. Studies of interfaces down to an atomic level are thus highly motivated both from a fundamental and technological point of view. In this thesis, a surface science approach has been employed to study the formation of interfaces in systems relevant for transistor and solar cell applications. Surface science methodology entails ultra high vacuum environment, single crystalline surfaces, submonolayer control of deposited material, surface sensitive spectroscopy and atomic resolution microscopy.

The primary experimental method for characterization is electron spectroscopy. This is a family of very powerful experimental techniques capable of giving information on the atomic level. Additionally, studies have been performed using scanning tunnelling microscopy. Combined these two methods can provide an atomic level characterisation of the geometric and electronic properties of the surface.

The emphasis of this work is placed on ultra thin TiO2 and ZrO2 films grown on silicon substrates by means of ultra-high vacuum metal-organic chemical vapour deposition. ZrO2 has also been grown on SiC and FeCrAl. Deposition has been performed with different process parameters. The interface region of each film has been characterised. The band alignment, a most important issue with regard to the development of new transistor devices, for the ZrO2/Si(100) system has been explored. Decomposition pathways of the metal organic precursors have been studied in detail. Changing process parameters is shown to alter both the precursor decomposition pathway and the nature of the interface region, thus opening the possibility to tailor the material function.

The titanium dioxide films grown in situ have shown to be excellent models of nanostructured electrode materials. In this spirit, interfaces of model systems for the solid-state dye-sensitized solar cell have been studied. Links between device performance and interface structure have been elucidated.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2006. 58 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 203
Keyword
Physics, chemical vapour deposition, high-k, metal oxides, silicon, dye-solid interface, metal organic, electron spectroscopy, scanning tunnelling microscopy, Fysik
Identifiers
urn:nbn:se:uu:diva-7088 (URN)91-554-6622-2 (ISBN)
Public defence
2006-09-29, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2006-09-04 Created: 2006-09-04 Last updated: 2012-10-09Bibliographically approved

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