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Electronic Structure and Optical Quality of Nanocrystalline Y2O3 Film
Surfaces and Interfaces on Silicon
E. J. Rubio,† V. V. Atuchin,*,‡,§,∥ V. N. Kruchinin,⊥ L. D. Pokrovsky,‡ I. P. Prosvirin,# and C. V. Ramana†
†
Department of Mechanical Engineering, University of Texas at El Paso, El Paso, Texas 79968, United States
Laboratory of Optical Materials and Structures, Institute of Semiconductor Physics, SB RAS, Novosibirsk 630090, Russia
§
Functional Electronics Laboratory, Tomsk State University, Tomsk 634050, Russia
∥
Laboratory of Semiconductor and Dielectric Materials, Novosibirsk State University, Novosibirsk 630090, Russia
⊥
Laboratory for Ellipsometry of Semiconductor Materials and Structures, Institute of Semiconductor Physics, SB RAS, Novosibirsk
630090, Russia
#
Boreskov Institute of Catalysis, SB RAS, Novosibirsk 630090, Russia
‡
S Supporting Information
*
ABSTRACT: Nanocrystalline yttrium oxide (Y2O3) thin films
were made by sputter deposition onto silicon (100) substrates
keeping the deposition temperature fixed at 300 °C. The
surface/interface chemistry, Y−O bonding, and optical
constants of the Y2O3 film surface and Y2O3−Si interface
were evaluated by the combined use of X-ray photoelectron
spectroscopy (XPS), depth-profiling, and spectroscopic
ellipsometry (SE). XPS analyses indicate the binding energies
(BEs) of the Y 3d doublet; i.e., the Y 3p5/2 and Y 3d3/2 peaks
are located at 117.0 and 119.1 eV, respectively, characterizing
yttrium in its highest chemical oxidation state (Y3+) in the
grown films. The optical model is constructed based on the
XPS depth profiles, which indicate that the Y2O3//Si
heterostructure can be represented with Y2O3 filmYxSiyOz interfacial compoundSi substrate. Such a model accounts for
the experimentally determined ellipsometry functions and accurately produces the dispersive index of refraction (n(λ)) of Y2O3
and YxSiyOz. The n(λ) of Y2O3 and YxSiyOz follows Cauchy’s dispersion relation, while the YxSiyOz formation accounts for
degradation of optical quality.
I. INTRODUCTION
Oxide dielectrics have been the subject of numerous
investigations for many years due to their possible device
integration in a wide range of technologies involving
electronics, electro-optics, optoelectronics, and magnetoelectronics.1−5 Yttrium oxide (Y2O3), a stable oxide of yttrium
metal, has received significant attention in recent years in view
of its possible integration into a wide range of scientific and
technological applications.6−12 Y2O3 films exhibit excellent
electronic properties such as transparency over a broad spectral
range (0.2−8 μm), high dielectric constant (∼14−18), high
refractive index (∼2), large band gap (∼5.8 eV), low absorption
(from near-UV to IR), and superior electrical breakdown
strength (>3 MV/cm).1,8−11,13−15 These properties make Y2O3
films interesting for various electrical and optical devices.16−22
Yttrium oxides were proposed as hosts for rare-earth elements,
and efficient thin film phosphors were prepared.23−29 The
interface layer formation, however, was detected for several
compounds, and structural and chemical parameters of the
interface were dependent on the deposition conditions.
Therefore, controlled growth and manipulation of micro© 2014 American Chemical Society
structure, particularly at the nanoscale dimensions, has
important implications for the design and applications of
Y2O3 films.
Yttrium oxide is a c-type rare-earth oxide.30 The c-type
structure of Y2O3 is stable up to 2325 °C in the air. The c-type
structure is a modified fluorite-type cubic structure with onefourth of the anion sites vacant and regularly arranged. The
structural stability coupled with mechanical properties also
make Y2O3 an interesting material for other applications.
Specifically, Y2O3 has been in use in the development of
functional ceramics for solid oxide fuel cells, nuclear engineering, high-temperature protective coatings, and metal-reinforced
composites for high strength structural components.31−35
A wide variety of physical and chemical deposition
techniques have been employed to fabricate Y2O3 films.
However, in both physical and chemical deposition methods,
the ultramicrostructure in terms of the chemical valence state of
Received: March 23, 2014
Revised: May 15, 2014
Published: May 30, 2014
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chamber to ignite the plasma. Once the plasma was ignited the
power was increased to 100 W, and oxygen (O2) was released
into the chamber for reactive deposition. The flow of the Ar
and O2 and their ratio were controlled using MKS mass flow
controllers. Before each deposition, the Y-target was presputtered for 10 min using Ar alone with the shutter above the gun
closed. The deposition was made keeping the substrate
temperature (Ts) at 300 °C, which was found to be optimum
to produce nanocrystalline Y2O3 films as reported elsewhere.11,15,20
B. Characterization. X-ray Photoelectron Spectroscopy
(XPS). Electronic properties of the Y2O3/Si system were
characterized by X-ray photoelectron spectroscopy. Depth
profiling of Y2O3 films on Si was performed with the standard
procedure, which is a combination of Ar+ ion sputtering/
bombardment followed by XPS data acquisition and analysis.39−41 The XPS valence-band and core-level spectra of Y2O3
were measured using the ultrahigh vacuum (UHV) AnalysisSystem assembled by SPECS (Germany). The system is
equipped with a PHOIBOS 150 hemispherical analyzer and Xray monochromator FOCUS-500. The Al Kα irradiation (hν =
1486.74 eV, 200 W) was used as a source of photoelectron
excitation. The survey spectrum was recorded at the analyzer
pass energy of 50 eV and the narrow spectral regions at 10 eV.
The atomic concentration ratios of elements on the sample
surface were calculated from the integral photoelectron peak
intensities and known atomic sensitivity factors (ASFs).42 The
energy scale of the spectrometer was calibrated by setting the
measured Au 4f7/2 and Cu 2p3/2 binding energies (BEs) to
84.00 ± 0.05 eV and 932.66 ± 0.05 eV, respectively, in
reference to the Fermi level. For the peak fitting procedure a
mixture of Lorenzian and Gaussian functions were used
together with the Shirley background subtraction method.
The film depth profiling was carried out using an argon ion gun
(SPECS model IQE 11/35). The energy of Ar+ ions for depth
profiling, the current density, and the angle of sputter erosion
were 1.05 keV, 4−5 μA/cm2, and 45°, respectively. The depth
profiling rate under these conditions was estimated as ∼0.3
nm/min in reference to the Al2O3/Al model film system.
Reflection High-Energy Electron Diffraction. The surface
crystallography of Y2O3 film was investigated using reflection
high-energy electron diffraction (RHEED) measurements. The
electron diffraction imaging was performed using a 50 keV
electron beam in the EF-Z4-5 (Carl Zeiss, Germany) setup.
Spectroscopic Ellipsometry (SE). The dispersive refractive
index n(λ) and extinction coefficient k(λ) were determined by
means of spectroscopic ellipsometry (SE). Ellipsometric angles
Ψ and Δ were measured as a function of λ in the spectral range
of λ ∼ 250−1030 nm using an ELLIPS-1771 SA ellipsometer.43
The instrumental spectral resolution was 2 nm, and the
recording time of the spectrum did not exceed 20 s. The SE
measurements were produced at three angles of incidence of
light beam on the sample of 50°, 60°, and 70°. The four-zone
measurement method was used with subsequent averaging over
all the four zones.44−46
Y and the surface/interface chemistry strongly influence the
electronic and optical properties of the grown films and, hence,
their device applications. Most importantly, determination of
the dispersive optical constants, namely, index of refraction (n)
and extinction coefficient (k), is important for Y2O3 films
deposited on semiconductor materials when chemical interaction with a substrate surface may influence the interface
properties. Furthermore, for thin films, the optical constants are
sensitive to the microstructure and are influenced by various
factors such as surface/interface structure, crystal quality,
packing density, lattice parameters, lattice strain, defect
structure, and chemical composition. Additionally, the quality
of the evolving film surface and interfacial compounds buried at
the film−substrate interface are quite important for oxide
dielectrics, such as Y2O3 in this case, for their effective
utilization in optical, electronic, and optoelectronic device
applications. The chemical reaction between the oxide dielectric
and Si substrate during fabrication or the postdeposition
annealing process resulting in the formation of interfacial layers
(ILs), with silicon oxide (SiO2), or metallic clusters of the
respective oxide dielectric, or metal-silicates, or a combination
of these has been widely reported.15,20,22,31 Interfacial chemical
compounds from the interfacial reaction suppress the effective
dielectric constant and optical quality and, hence, device
performances.1,8 Therefore, understanding the electronic
structure and optical quality of the Y2O3 film surface and
interface is quite important. The present work was, therefore,
performed on sputter-deposited Y-oxide films made by sputterdeposition onto Si substrates to probe their surface chemistry,
Y−O bonding, and optical constants. Combined X-ray
photoelectron spectroscopy (XPS) with depth profiling and
spectroscopic ellipsometry (SE) measurements, as presented
and discussed in this paper, allowed us to determine the
surface/interface chemical composition, nature of the interfacial
chemical compounds, and optical constants of nanocrystalline
Y2O3 films and interfacial compounds at the Y2O3−Si interface.
II. EXPERIMENTS
A. Fabrication. Yttrium oxide (Y2O3) thin films were
deposited onto silicon (Si) (100) wafer substrates by radio
frequency (RF) (13.56 MHz) reactive magnetron sputtering.
All the substrates were thoroughly cleaned using the RCA
(Radio Corporation of America) procedure.36−38 Briefly, the
RCA cleaning procedure removes organic, alkali ions, and
heavy metal contaminants present on the surface of the
substrate. The cleaning procedure has three major steps. (1)
Removal of insoluble organic contaminants using 5:1:1 H2O/
H2O2/NH4OH solution. (2) Removal of ionic and heavy metal
atomic components using a solution of 6:1:1 H2O/H2O2/HCl
solution. (3) Removal of native oxide by buffered oxide etching
solution. At the stage, a Kikkuchi pattern was recorded
commonly from Si substrates by RHEED measurements.
Finally, the substrates were dried with nitrogen before
introducing them into the vacuum chamber. After this, the
substrates were transferred to a magnetron sputtering chamber
through the laboratory air because we do not have an isolated
substrate transport system. The vacuum chamber was initially
evacuated to a base pressure of ∼10−6 Torr. An yttrium (Y)
target (Plasmaterials Inc.) of 2” diameter and 99.95% purity was
employed for reactive sputtering. The Y-target was placed on a
2-in. sputter gun, which is placed at the distance of 8 cm from
the substrate. A sputtering power of 40 W was initially applied
to the target while introducing high purity argon (Ar) into the
III. RESULTS AND DISCUSSION
The RHEED pattern of Y2O3 films grown at 300 °C is shown in
Figure 1. The formation of a well-defined ring structure
indicative of Y2O3 film of polycrystalline nature is evident from
the RHEED pattern shown in Figure 1. The observed electron
diffraction pattern matches the cubic-Y2O3 (JCPDS 43-613).47
The detailed XRD data and RHEED analysis of Y2O3 films as a
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Figure 1. RHEED pattern recorded from Y2O3/Si film.
function of variable Ts were reported elsewhere.20,22 Briefly, the
XRD and RHEED analyses indicate that the Y2O3 films grown
at 25−100 °C were amorphous (a-Y2O3) in nature. The onset
of crystallization with a (222) peak in XRD patterns
corresponding to the cubic phase (c-Y2O3) began to appear
for the Y2O3 samples grown at Ts = 200 °C. The peak intensity
increases with the increasing Ts, indicating an increase in the
average grain size with the increasing Ts. The present RHEED
data confirm the crystalline nature of the Y2O3 films grown on
Si(100) substrates.
To obtain the surface and interface chemistry and accurately
determine the optical constants, the Y2O3 film was sputtered all
along the depth of the film until the signature of the Si
substrate, while the surface/interface chemical composition was
probed with XPS. The survey photoemission spectrum
recorded from the initial surface is shown in Figure S1
(Supporting Information). Besides constituent element core
levels and Auger lines related to Y2O3 oxide, the C 1s core level
and C KVV Auger line were detected and attributed to
adventitious hydrocarbons adsorbed from the air.
The detailed photoemission peaks of Y 3d, Si 2p, and O 1s
levels are shown in Figures 2−4. All the spectra are shown as a
function of sputtering time of the Y2O3//Si heterostructure.
Figure 3. Si 2p core-level XPS spectra.
Figure 4. O 1s core-level XPS spectra.
The integrated sputtering (etching) time is as indicated in the
XPS curves in Figures 2−4. The initial time setting (t = 0)
corresponds to most of the film top surface (as-grown). When
the top surface contaminated layer was sputtered by ion
bombardment, in the film bulk, the binding energy (BE)
position of the Y 3d doublet (Y 3d5/2 and Y 3d3/2) and O 1s
line occurred at 157.0, 159.1, and 529.2 eV, respectively
(Figures 2 and 4). The BE values can be compared to those
earlier reported for the Y2O3 oxide. However, an observation of
available electronic parameters of this functional oxide reveals a
drastic scattering of BE values in the literature. The
Figure 2. Si 2s−Y 3d core-level XPS spectra.
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in Figures 2, 3, and 5. The most interesting feature is that, at t >
80 min, the Si 2p (BE ∼ 99.3 eV) and Si 2s (BE ∼ 150.4 eV)
lines appear due to the presence of elemental Si0.42,61
Furthermore, the BE value of the Si 2p line remains constant
up to the substrate. Simultaneously, at t = 80−90 min, the small
intensity signal at 102.8 eV is recorded in the Si 2p core-level
spectra shown in Figure 3. This line, in accordance with the
energy difference ∼3.5 eV, in reference to the Si 2p (BE ∼ 99.3
eV) line from Si0, should be attributed to Si4+ states.61−63 As for
Y 3d5/2 and O 1s levels, at t > 80 min, the lines shift to higher
energies. The O 1s band can be subdivided into two
components at ∼530.4 and ∼532 eV. The low-energy
component indicates the value of ΔBEY = BE (O 1s) − BE
(Y 3d5/2) = 372.2 eV, which can be attributed to the Y−O−Si
bonding. The higher-energy component in the O 1s band may
be related to interfacial carbonate species because the increased
C 1s line intensity is found at t = 80−90 min. All film
components disappeared at t = 140 min, which relates to a film
thickness of ∼42 nm.
Y2O3/Si film optical constants were primarily probed by
spectroscopic ellipsometry (SE), which measures the relative
changes in the amplitude and phase of the linearly polarized
monochromatic incident light upon the oblique reflection from
the sample surface. Ellipsometric parameters Ψ and Δ are
related to the complex Fresnel reflection coefficients by the
equation
accumulated set of BE values of Y 3d5/2 and O 1s lines in Y2O3,
together with BE difference ΔBEY = BE (O 1s) − BE (Y 3d5/2),
is shown in Table 1. As found for many chemical classes of
Table 1. BE Values of Representative Constituent Element
Lines in Y2O3
state
BE (Y 3d5/2),
eV
BE (O 1s),
eV
ΔBEY,
eV
ref
ceramics
film
film
film
film
film
film
film
nanocrystals
film
film
156.7
158.5
155.5
156.5−157.0
156.6
156.0
158.1
158.4
156.7
156.6
156.2
157.0
529.5
530.6
527.7
529.0
529.0
530.2
529.7
529.5
528.4
529.2
372.8
372.1
372.2
372.4
373.0
372.1
371.3
372.8
372.2
372.2
6
6
22
42
48
49
50
51
52
53
54
present study
oxides, the BE difference parameters are insensitive to surface
charging effects and BE scale calibration methods, and they are
particularly suitable for the comparative analysis of XPS results
measured by different spectrometers.55−60 In Table 1, the
scattering of BE (Y 3d5/2) and BE (O 1s) values is as high as 3.0
and 2.9 eV which is evidently above any physically conditioned
range. Comparatively, the scattering range of ΔBEY is as low as
1.7 eV. Moreover, this scattering can be further decreased by
simple selection. The highest and lowest ΔBEY values appeared
from refs 49 and 51, and this indicates an inexact energy scale
calibration. If we exclude the results, the scattering range of
ΔBEY becomes as narrow as 0.7 eV. The value obtained in the
present study is in good agreement with stoichiometric Y2O3
and characterizes the yttrium ions in their highest oxidation
state (Y3+).
The calculated atomic concentrations are shown as a
function of depth in Figure 5. As is evident from Figures
2−4, over the range of t = 3−60 min, the composition of the
film bulk is stable and well related to stoichiometric Y2O3. The
change in chemical composition is evident at t > 60 min, where
the signals of yttrium and oxygen decrease while the silicon
signal increases. The evolution of the Si signal and
concentration as a function of time/depth can be clearly seen
tg Ψ·eiΔ =
Rp
Rs
(1)
where Rp and Rs are the coefficients for p- and s-polarized light
waves. To calculate the dependencies of refractive index n(λ)
and extinction coefficient k(λ) on optical wavelength λ, the
experimental data were processed using the multilayer model.
Over the whole spectral range, the spectral dependences of
polarization angles were fitted for m points of the spectrum by
minimization of the error function
m
σ2 =
1
· ∑ [(Δexptl − Δcalcd )2 + (Ψexptl − Ψcalcd)2 ]
m i=1
(2)
Extracting meaningful physical information from ellipsometry
requires the construction of an optical model of the sample
which generally has a number of distinct layers with individual
optical dispersions. Interfaces between these layers are optical
boundaries at which light is refracted and reflected according to
the Fresnel relations. In the present case, to determine the
dispersive optical constants accurately, the optical model of the
Y2O3/Si system is constructed based on the XPS depth
profiling results.64,65 The model contains the Y2O3 top layer,
multicomponent multilayer system, and the Si substrate. The
optical model is schematically shown in Figure 6, while the
layer composition is summarized in Table 2. The thickness and
chemical composition of each layer are basically derived from
XPS data with the following key points taken into
consideration. As seen from Figure 5, at t < 60 min the film
is completely formed by pure Y2O3 oxide with the thickness of
∼18 nm. Between the Y2O3 layer and Si substrate, the bulk of
the interface film is modeled as a set of six sublayers with a
different composition. The thickness of each sublayer between
the Y2O3 film and Si substrate was directly estimated from the
XPS sputtering rate. The atomic composition of each layer is
taken as the averaged value of boundary XPS measurements.
Principally, the whole system is represented as the (Y2O3
Figure 5. Elemental near surface composition as a function of depth.
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n(λ) = a +
b
c
+ 4
2
λ
λ
({3})
For the calculations of the multilayer system, the Bruggeman
effective medium model was used
⎛
εi − εeff ⎞
⎟=0
⎝ εi − 2·εeff ⎠
∑ ⎜fi
i
({4})
where f i and εi are the part and dielectric permittivity of the icomponent and εeff is the effective dielectric permittivity of the
medium.68 The calculation results are shown in Figures 7 and 8.
Figure 6. Optical model of the reflection system constructed based on
the XPS results.
Table 2. Thickness and Phase Composition of the Sublayers
Considered in Ellipsometric Model
layer
layer thickness, nm
β Si
β Y2O3
β YxSiyOz
1
2
3
4
5
6
7
6
3
3
3
3
6
18
0.914
0.862
0.747
0.521
0.290
0.105
0
0.004
0.130
0.218
0.419
0.654
0.870
1
0.082
0.008
0.035
0.06
0.056
0.025
0
film)−(YxSiyOz + Si interfacial composite)−(Si substrate)
system.
The experimental and calculated Ψ(λ), Δ(λ) curves obtained
for the Y2O3/Si multilayered system are shown in Figure 7.
Figure 8. Dispersive n(λ) of Y2O3 (1) and YxSiyOz (2). Curve (3)
calculated in the homogeneous layer approximation.
The best correlation between the experimental and
calculated Ψ(λ), Δ(λ) curves (1) in Figure 7 is achieved at
the best optical dispersion of YxSiyOz interfacial oxide, as
represented by curve (2) in Figure 8. The drastic difference,
however, is evident between experimental points and Ψ(λ),
Δ(λ) curves (2) in Figure 7 calculated using the model of single
homogeneous transparent layer. The refractive index dispersion
calculated in the framework of a single homogeneous
transparent layer is shown by curve (3) in Figure 8. Thus,
the simple reflection model of a single homogeneous layer is
principally not applicable for the adequate description of the
real Y2O3/Si layered system. The refractive index dispersion in
YxSiyOz obtained in the framework of the multilayer reflection
model is defined by Cauchy’s polynomial (3) with parameters a
= 1.749, b = 6.76 × 103, and c = −8.3 × 107. The refractive
index of oxide YxSiyOz is noticeably lower than that of Y2O3
over the spectral range observed. For comparison, the n(λ)curve (3) calculated using the single homogeneous transparent
layer model (Figure 8) indicates very low refractive index
values, but a little higher than those of pure SiO2.
The significance of our present approach and model can be
understood as follows. Several optical models were tested for
the Y2O3/Si layered system in the literature. The multilayer
stack of (surface roughened Y2O3 layer)−(Y2O3 bulk layer)−
(SiO2 interface layer)−(Si substrate) was proposed in ref 54.
However, a very strange refractive index dispersion has been
found for the Y2O3 oxide formed by Y2O3 target sputtering in
the (Ar + O2) mixture.54 The dispersion is very strong over the
Figure 7. Dispersive ellipsometric parameters Ψ(λ), Δ(λ): (1)
recorded for the layer system Y 2O3/Si. Experiment: points.
Calculations: curve. (2) Calculated in homogeneous layer approximation.
Dispersive optical constants of Si and Y2O3 were taken from
refs 66 and 67, respectively. The inverse ellipsometric problem
was solved for compound YxSiyOz with a fixed composition to
generate the n(λ) function. It was supposed that the n(λ)
function of YxSiyOz falls between the n(λ) functions of SiO2 and
Y2O3. The n(λ) functions of Y2O3 and YxSiyOz were
approximated by Cauchy’s polynomials
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spectral range of 200−500 nm and is practically absent at
longer wavelengths. The results are not at all in correlation with
the available dispersion properties of the Y2O3 bulk.67 In
addition, the refractive index of Y2O3 films was found to
decrease with (Ar + O2) pressure increase and under better
oxidative conditions. The SE method was applied for the
determination of optical parameters of oxide films prepared by
Y2O3 sputtering in ref 69. For the film formed at 700 °C, the
refractive index dispersion was found to be close to that of Y2O3
bulk. However, the optical model used for SE calculations was
not reported in detail.69 Gibbson et al. have used the multilayer
model for the SE determination of optical parameters of thick
Y2O3/Si films prepared by molecular beam epitaxy.70 The
model was able to account accurately for the thick MBE grown
Y2O3 films on Si. Using real-time monitoring, it was found that
interface layer accounting is insignificant for a Y2O3 film
thickness of ∼133 nm.70 However, as shown in the present
study, the interfacial compound formation and interface
properties are principal for thin (∼40 nm) oxide films, where
the thickness of the Y2O3 bulk of the film is comparable to the
interface layer thickness.
In the present study, the appearance of silicon in the Si0 state
in the interface layer is detected by XPS depth profiling and
verified by SE calculations for consistency. It is interesting to
consider possible source(s) of silicon incorporated into
interfacial oxide YxSiyOz. A SiO2 layer may be formed on the
surface of the silicon substrate due to the contact with the air
and oxidative atmosphere in a vacuum chamber. Then, at initial
stages of Y target sputtering, the silicon oxide layer was partly
reduced to the Si0 state by chemical interaction with active
yttrium atoms. The silicon atoms agglomerate into nanocrystals
leading to the formation of the YxSiyOz + Si interfacial
composite. The agglomeration of silicon atoms in nanocrystals
in the oxide host medium is a well-known effect in thin-film
formation on Si.71−74 As it appears from our data, this reaction
dominates at initial film formation stages. In parallel, the top
layer of Y2O3 bulk forms by yttrium target reactive sputtering.
Further oxidation of the silicon substrate and Si nanocrystals is
provided by oxygen diffused through the Y2O3 top layer, and
this mechanism offers the YxSiyOz interfacial oxide formation.
Article
ASSOCIATED CONTENT
S Supporting Information
*
Survey XPS spectrum. This material is available free of charge
via the Internet at http://pubs.acs.org.
■
AUTHOR INFORMATION
Corresponding Author
*E-mail: [email protected] (V. V. Atuchin). Phone: +7 (383)
3308889. Fax: +7 (383) 3332771.
Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS
Authors at University of Texas at El Paso acknowledge with
pleasure the support from NSF; NSF-PREM grant # DMR1205302. This study is partly supported by the Ministry of
Education and Science of the Russian Federation.
■
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IV. CONCLUSIONS
The depth profiling of the Y2O3/Si layer system produced by
Ar+ ion bombardment and XPS measurements yields detailed
information on the chemical composition and thickness needed
for the construction of an adequate optical model of the
reflection system. This optical model was applied for the
calculations of dispersive optical parameters of the interfacial
YxSiyOz oxide formed at the substrate temperature of 300 °C.
Now, the results can be used as a basis for accurate SE
determination of the Y2O3/Si layer thickness and interface
control. Furthermore, the formation of a YxSiyOz + Si
composite is found by core level photoemission spectroscopy.
As it is supposed, the silicon nanocrystals are generated by
chemical reaction of yttrium and the SiO2 layer on the substrate
surface resulted in silicon reduction up to the Si0 state. This
new effect may be of general significance for high-k dielectrics
based on Y and rare-earth elements because of similar chemical
properties. It is expected that these observations and model
made for Y2O3/Si films may be applicable to a large class of
similar layered systems, such as rare-earth oxide films grown on
Si, SiGe, and Ge substrates.
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