ISSN:
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2024
International scientific journal
«MODERN
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АND RESEARCH»
VOLUME 3 / ISSUE 2 / UIF:8.2 / MODERNSCIENCE.UZ
68
COMPOSITION AND MORPHOLOGY OF THE SURFACE OF Si (111) WITH
SURFACE FILM OF SiO2 OF DIFFERENT THICKNESS
A.A. Mustafoev
Jizzakh Polytechnic Institute
https://doi.org/10.5281/zenodo.10629023
Abstract. The composition, morphology, and electronic structure of SiO
2
nanofilms of
different thicknesses created by thermal oxidation on the Si(111) surface were studied in this work.
It was shown that up to a thickness of 30-40 Å the film has an island character. At d ≥ 60 Å, a
homogeneous continuous film of SiO
2
is formed, the stoichiometric surface roughness does not
exceed 1.5 – 2 nm. Regardless of the thickness of the SiO
2
films, no noticeable interdiffusion of
atoms is observed at the SiO
2
-Si boundary. The patterns of changes in the composition, the degree
of surface coverage, and the energy of plasma oscillations were determined when the thickness of
the SiO
2
/Si(111) films varied from 20 to 120 Å.
Key words: thermal oxidation, nanophases, nanofilms, plasma oscillation, surface
roughness, Auger peaks, Raman spectra, optical-phonon mode, island growth.
СОСТАВ И МОРФОЛОГИЯ ПОВЕРХНОСТИ Si(111) С ПОВЕРХНОСТНОЙ
ПЛЕНКОЙ SiO2 РАЗНОЙ ТОЛЩИНЫ
Аннотация. В работе исследованы состав, морфология и электронная структура
нанопленок SiO2 различной толщины, созданных термическим окислением на поверхности
Si(111). Показано, что до толщины 30–40 Å пленка имеет островной характер. При d ≥ 60
Å формируется однородная сплошная пленка SiO2, стехиометрическая шероховатость
поверхности не превышает 1,5 – 2 нм. Независимо от толщины пленок SiO2 заметной
взаимной диффузии атомов на границе SiO2-Si не наблюдается. Определены
закономерности изменения состава, степени покрытия поверхности и энергии плазменных
колебаний при изменении толщины пленок SiO2/Si(111) от 20 до 120 Å.
Ключевые слова: термическое окисление, нанофазы, нанопленки, плазменные
колебания, шероховатость поверхности, оже-пики, спектры комбинационного рассеяния
света, оптико-фононная мода, рост островков.
Introduction
Heterofilm structures of the SiO2/Si type and multilayer systems based on them are widely
used and promising for the creation of new solid-state electronics devices, in particular, in the
development of ultra-high-frequency MOS transistors, integrated circuits, memory elements and
displays, photoconverters, solar cells, etc. Such structures They are mainly created by methods of
thermal oxidation, ion-plasma deposition, and ion implantation.
Currently, the composition, structure and properties of SiO2/Si films of various thicknesses
obtained by various methods have been well studied [1-5]. In this case, the most uniform nanofilms
(d ≤ 50-60 Å) of SiO2, as in the case of metal silicides [6-9], were obtained by the method of low-
energy ion implantation in combination with annealing [4, 5].
The presence of excess silicon atoms or clusters in thin films of SiO
2
and metal silicides
leads to a significant change in their physical properties [10-12]. In the case of thin films (d ≤ 10
ISSN:
2181-3906
2024
International scientific journal
«MODERN
SCIENCE
АND RESEARCH»
VOLUME 3 / ISSUE 2 / UIF:8.2 / MODERNSCIENCE.UZ
69
nm) SiO
2
/Si, diffusion of Si atoms into the SiO2 film can occur. However, there is still no reliable
information about the dynamics of changes in the morphology, composition, crystalline and
electronic structure of SiO
2
/Si nanofilms with a thickness from d ≈ 20 Å to 100 Å, obtained by
thermal oxidation. Solving this problem was the main goal of this work.
Experimental technique
The objects of study were amorphous SiO
2
films created on the Si(111) surface by thermal
oxidation in a dry oxygen atmosphere. Studies of the composition, electronic structure, emission
and optical properties were carried out using the methods of Auger electron spectroscopy (AES),
characteristic electron energy loss spectroscopy (CHLES), ultraviolet photoelectron spectroscopy
(UFES) on the same ultra-high vacuum device at P = 10
-7
Pa.
The surface morphology and crystal structure were studied using standard scanning
electron microscopy SUPRA-40, atomic force microscopy (XE-200) and Raman spectrometer.
The depth distribution profiles of atoms were recorded using the OES method in combination with
surface etching with Ar
+
ions.
Films with thickness d = 20, 40, 60, 80, 100 and 500 Å were mainly used. Before the study,
the samples were evacuated at T = 900 K for 4-5 hours at a pressure of at least 10
-7
Pa.
Results of experiments and their discussions
In Fig. Figure 1 shows an SEM image of the surface of a SiO2/Si film with d ≈ 20 Å. It can
be seen that the film has an island character.
Fig. 1. SEM image of the surface of a Si film with a SiO
2
film 20 Å thick.
The average surface dimensions of the islands are 40–50 nm. Further studies showed that
with increasing oxidation time, the sizes of the islands increase; starting from d ≈ 40 Å, the
boundaries of neighboring islands overlap and a continuous SiO
2
film is formed.
In Fig. Figure 2 shows Auger spectra of SiO
2
/Si(111) films of different thicknesses,
recorded in the region E ≈ 70-100 eV.
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Fig. 2. Auger electron spectra of Si(III) with SiO
2
nanofilm of different thicknesses
d, Å: 1-0; 2-20; 3-40; 4-80
Auger spectra were recorded at the primary beam electron energy Ep = 2500 eV. Already
at d = 20 Å, a low-intensity SiO
2
peak with E ≈ 76 eV appears in the Auger spectrum. As d
increases, the intensity of the SiO
2
peak increases and at d ≈ 60 Å reaches its maximum value, and
the intensity of the Si peak decreases to zero (within the sensitivity of the Auger spectrometer).
Fig.3. Dependence of the intensity of the Auger peak of SiO
2
(E = 76 eV) on the thickness
of the SiO
2
film
As can be seen from Fig. 3, the intensity of ISiO
2
increases almost linearly up to d ≈ 40 Å,
and exponentially in the range d = 40-80 Å. At d > 80 Å, the intensity of ISiO
2
remains virtually
unchanged, and the Auger peak of pure Si completely disappears. Analysis of Auger electron
spectra together with SEM images showed that in the range d ≈ 0-40 Å the linear growth of ISiO
2
is mainly associated with an increase in the size of surface islands, i.e. with the degree of coverage
of the Si surface with SiO
2
islands. Due to the fact that at d ≈ 40 Å a continuous film of SiO
2
begins
to form, the increase in ISiO
2
in the range d ≈ 40-80 Å is explained by a decrease in the influence
of the substrate (silicon) on the yield of secondary electrons. At d ≥ 80 Å, Auger electrons emerge
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only from the SiO2 film. From these data it is clear that in the case of thin SiO
2
/Si films, no
noticeable diffusion of substrate atoms into the oxide film occurs.
HPEE spectra also provide rich information about the surface composition and the density
of state of the valence electrons. In particular, measuring plasmon energy can serve to identify
samples. In Fig. Figure 4 shows the SEE of SiO
2
/Si(111) films of different thicknesses.
Fig. 4. Si XPEE with SiO2 film with thickness d, Å: 1-0; 2-20; 3-40; 4-60.
It can be seen that with increasing film thickness, the contribution of Si (substrate) to the
yield of electrons with characteristic losses decreases, and that from the SiO2 film increases
accordingly. At dSiO
2
= 20 Å, along with the intense peaks of plasma vibrations (hωs, hωv, 2hωs)
of Si, a low-intensity peak of the bulk plasmon SiO2 with E ≈ 22 eV appears in the spectrum. As
d increases, the intensity of this peak increases, and the intensity of the Si peaks decreases. Starting
from d = 40 Å, another peak is detected at E = 14.5 eV, associated with the excitation of the SiO2
surface plasmon. Apparently, the excitation of the SiO2 surface plasmon occurs after the formation
of a continuous film. At d ≈ 60 Å, the CPEE spectrum characteristic of bulk SiO2 films is
completely established.
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Fig. 5. Raman spectra of Si(111) with a SiO2 film 100 Å thick.
In Fig. Figure 5 shows the Raman spectra of Si(111) with a SiO2 film 100 Å thick. It can
be seen that at ~520 cm
-1
a very intense peak of the optical phonon mode of pure single-crystal
Si is detected. The peak of the optical phonon mode of Si of the second order ( 943 – 980 cm
-1
)
is greatly broadened, which is associated with the presence of a thin amorphous layer of SiO
2
on
the Si surface.
Conclusion
Based on the analysis of the results obtained in the work, the following conclusions can
be drawn: SiO2 films obtained by the method of thermal oxidation of Si to a thickness of -40 Å
have an island character; at d ≥ 60 Å, a continuous amorphous homogeneous film is formed. In
all cases, the SiO2 films have good stoichiometry and no interdiffusion of atoms is observed at
the SiO2/Si(111) interface. Already at a thickness of 20 Å, a peak appears in the CPEE spectrum
at ΔE ≈ 22 eV, characteristic of the bulk plasmon of SiO2, and at a thickness of 40 Å, a peak of
surface plasmon.
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