Nucleation and crystallisation of hafnium compounds and thin films
Author(s)
McVicar McGilvery , Catriona
Type
Thesis
Abstract
Hafnia and hafnium silicate are leading high-κ materials to replace SiO2 in CMOS
devices. In this thesis the results of a study of bulk powders and thin films of these
materials are reported.
Bulk powders were investigated to provide a greater understanding of the crystallisation
process by which HfO2 and HfSiO4 are formed. Investigation using thermal analysis, xray
diffraction and electron microscopy techniques revealed that starting materials,
heating conditions and atmosphere significantly affected the crystallisation pathway. In
particular three mechanisms for tetragonal hafnia (t-HfO2) stabilisation were identified:
(1) oxygen vacancies; (2) the critical particle size effect; and (3) the surface energy
effect.
Electron energy-loss spectroscopy (EELS) was used to try to obtain a standard
O K edge for t-HfO2 from the powders and to better understand experimental EELS
spectra obtained from thin films. A standard t-HfO2 edge was not found and many of
the spectra obtained did not match existing standard edge shapes. The local atomic
environment has a large effect on the edge shape in these samples, leading to the
conclusion that a ‘standard’ edge shape may be impossible to obtain. Combining the
EELS spectra from bulk and thin film samples, with modelled data it was found that the
atoms within ~6Å from the excited atom had the largest effect on the edge shape.
Consequently EELS spectra taken at a distance from an interface greater than ~6Å will
give a bulk-like signal.
20nm HfxSi1-xO2 thin films were also investigated using TEM having been subjected to
different thermal anneals and deposition conditions. It was found that the electron beam
caused significant growth of SiO2 layers due to oxygen diffusion, and crystallisation
within the high-κ layer. Furthermore, the higher the SiO2 content in the sample the
more crystallisation was inhibited, though segregation into HfO2 and SiO2 rich regions
occurred in all samples.
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devices. In this thesis the results of a study of bulk powders and thin films of these
materials are reported.
Bulk powders were investigated to provide a greater understanding of the crystallisation
process by which HfO2 and HfSiO4 are formed. Investigation using thermal analysis, xray
diffraction and electron microscopy techniques revealed that starting materials,
heating conditions and atmosphere significantly affected the crystallisation pathway. In
particular three mechanisms for tetragonal hafnia (t-HfO2) stabilisation were identified:
(1) oxygen vacancies; (2) the critical particle size effect; and (3) the surface energy
effect.
Electron energy-loss spectroscopy (EELS) was used to try to obtain a standard
O K edge for t-HfO2 from the powders and to better understand experimental EELS
spectra obtained from thin films. A standard t-HfO2 edge was not found and many of
the spectra obtained did not match existing standard edge shapes. The local atomic
environment has a large effect on the edge shape in these samples, leading to the
conclusion that a ‘standard’ edge shape may be impossible to obtain. Combining the
EELS spectra from bulk and thin film samples, with modelled data it was found that the
atoms within ~6Å from the excited atom had the largest effect on the edge shape.
Consequently EELS spectra taken at a distance from an interface greater than ~6Å will
give a bulk-like signal.
20nm HfxSi1-xO2 thin films were also investigated using TEM having been subjected to
different thermal anneals and deposition conditions. It was found that the electron beam
caused significant growth of SiO2 layers due to oxygen diffusion, and crystallisation
within the high-κ layer. Furthermore, the higher the SiO2 content in the sample the
more crystallisation was inhibited, though segregation into HfO2 and SiO2 rich regions
occurred in all samples.
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Date Issued
2008
Date Awarded
2008-11
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Craven, Alan
McComb, David
Creator
McVicar McGilvery , Catriona
Publisher Department
Department of Materials
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)