Polarization conversion effect in obliquely deposited SiOx films
Structural anisotropy of the SiOx films and nc-Si-SiOx light emitting nanostructures, prepared by oblique deposition of silicon monoxide in vacuum, has been studied using the polarization conversion (PC) effect. For this purpose, a simple method of PC investigation with usage of a standard null-ell...
Gespeichert in:
| Veröffentlicht in: | Semiconductor Physics Quantum Electronics & Optoelectronics |
|---|---|
| Datum: | 2011 |
| Hauptverfasser: | , , , , |
| Format: | Artikel |
| Sprache: | English |
| Veröffentlicht: |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2011
|
| Online Zugang: | https://nasplib.isofts.kiev.ua/handle/123456789/117749 |
| Tags: |
Tag hinzufügen
Keine Tags, Fügen Sie den ersten Tag hinzu!
|
| Назва журналу: | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| Zitieren: | Polarization conversion effect in obliquely deposited SiOx films / M.V. Sopinskyy, I.Z. Indutnyi, K.V. Michailovska, P.E. Shepeliavy, V.M. Tkach // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2011. — Т. 14, № 3. — С. 273-278. — Бібліогр.: 21 назв. — англ. |
Institution
Digital Library of Periodicals of National Academy of Sciences of Ukraine| id |
nasplib_isofts_kiev_ua-123456789-117749 |
|---|---|
| record_format |
dspace |
| spelling |
Sopinskyy, M.V. Indutnyi, I.Z. Michailovska, K.V. Shepeliavyi, P.E. Tkach, V.M. 2017-05-26T15:57:07Z 2017-05-26T15:57:07Z 2011 Polarization conversion effect in obliquely deposited SiOx films / M.V. Sopinskyy, I.Z. Indutnyi, K.V. Michailovska, P.E. Shepeliavy, V.M. Tkach // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2011. — Т. 14, № 3. — С. 273-278. — Бібліогр.: 21 назв. — англ. 1560-8034 PACS 78.20.-e, 81.15-z https://nasplib.isofts.kiev.ua/handle/123456789/117749 Structural anisotropy of the SiOx films and nc-Si-SiOx light emitting nanostructures, prepared by oblique deposition of silicon monoxide in vacuum, has been studied using the polarization conversion (PC) effect. For this purpose, a simple method of PC investigation with usage of a standard null-ellipsometer is proposed and tested. This method is based on the analysis of the azimuthal angle dependence of the offdiagonal elements of the Jones matrix. The electron microscopy study shows that obliquely deposited SiOx films have a porous (column-like) structure with the column diameter and inclination depending on the deposition angle. Polarimetric investigations revealed that both in-plane and out-of-plane anisotropy was present, which is associated with the columnar growth. The correlation between the PC manifestations and the scanning electron microscopy results is analyzed. It was found that the tilt angle of columns in obliquely deposited SiOx is smaller than that predicted by the “tangent rule” and “cosine rule” models, and depends on the crystallographic orientation of Si substrate. It is concluded that the proposed method is effective non-destructive express technique for the structural characterization of obliquely deposited films. en Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України Semiconductor Physics Quantum Electronics & Optoelectronics Polarization conversion effect in obliquely deposited SiOx films Article published earlier |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| title |
Polarization conversion effect in obliquely deposited SiOx films |
| spellingShingle |
Polarization conversion effect in obliquely deposited SiOx films Sopinskyy, M.V. Indutnyi, I.Z. Michailovska, K.V. Shepeliavyi, P.E. Tkach, V.M. |
| title_short |
Polarization conversion effect in obliquely deposited SiOx films |
| title_full |
Polarization conversion effect in obliquely deposited SiOx films |
| title_fullStr |
Polarization conversion effect in obliquely deposited SiOx films |
| title_full_unstemmed |
Polarization conversion effect in obliquely deposited SiOx films |
| title_sort |
polarization conversion effect in obliquely deposited siox films |
| author |
Sopinskyy, M.V. Indutnyi, I.Z. Michailovska, K.V. Shepeliavyi, P.E. Tkach, V.M. |
| author_facet |
Sopinskyy, M.V. Indutnyi, I.Z. Michailovska, K.V. Shepeliavyi, P.E. Tkach, V.M. |
| publishDate |
2011 |
| language |
English |
| container_title |
Semiconductor Physics Quantum Electronics & Optoelectronics |
| publisher |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| format |
Article |
| description |
Structural anisotropy of the SiOx films and nc-Si-SiOx light emitting nanostructures, prepared by oblique deposition of silicon monoxide in vacuum, has been studied using the polarization conversion (PC) effect. For this purpose, a simple method of PC investigation with usage of a standard null-ellipsometer is proposed and tested. This method is based on the analysis of the azimuthal angle dependence of the offdiagonal elements of the Jones matrix. The electron microscopy study shows that obliquely deposited SiOx films have a porous (column-like) structure with the column diameter and inclination depending on the deposition angle. Polarimetric investigations revealed that both in-plane and out-of-plane anisotropy was present, which is associated with the columnar growth. The correlation between the PC manifestations and the scanning electron microscopy results is analyzed. It was found that the tilt angle of columns in obliquely deposited SiOx is smaller than that predicted by the “tangent rule” and “cosine rule” models, and depends on the crystallographic orientation of Si substrate. It is concluded that the proposed method is effective non-destructive express technique for the structural characterization of obliquely deposited films.
|
| issn |
1560-8034 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/117749 |
| citation_txt |
Polarization conversion effect in obliquely deposited SiOx films / M.V. Sopinskyy, I.Z. Indutnyi, K.V. Michailovska, P.E. Shepeliavy, V.M. Tkach // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2011. — Т. 14, № 3. — С. 273-278. — Бібліогр.: 21 назв. — англ. |
| work_keys_str_mv |
AT sopinskyymv polarizationconversioneffectinobliquelydepositedsioxfilms AT indutnyiiz polarizationconversioneffectinobliquelydepositedsioxfilms AT michailovskakv polarizationconversioneffectinobliquelydepositedsioxfilms AT shepeliavyipe polarizationconversioneffectinobliquelydepositedsioxfilms AT tkachvm polarizationconversioneffectinobliquelydepositedsioxfilms |
| first_indexed |
2025-11-26T00:08:25Z |
| last_indexed |
2025-11-26T00:08:25Z |
| _version_ |
1850592156970909696 |
| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2011. V. 14, N 3. P. 273-278.
PACS 78.20.-e, 81.15-z
Polarization conversion effect in obliquely deposited SiOx films
M.V. Sopinskyy1, I.Z. Indutnyi1, K.V. Michailovska1, P.E. Shepeliavyi1, V.M. Tkach2
1V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine,
45, prospect Nauky, 03028 Kyiv, Ukraine
2V. Bakul Institute for Superhard Materials, NAS of Ukraine,
2, Avtozavodska str., 04074 Kyiv, Ukraine
E-mail: sopinsky@isp.kiev.ua
Abstract. Structural anisotropy of the SiOx films and light emitting
nanostructures, prepared by oblique deposition of silicon monoxide in vacuum, has been
studied using the polarization conversion (PC) effect. For this purpose, a simple method
of PC investigation with usage of a standard null-ellipsometer is proposed and tested.
This method is based on the analysis of the azimuthal angle dependence of the off-
diagonal elements of the Jones matrix. The electron microscopy study shows that
obliquely deposited SiO
xSiOSi-nc −
x films have a porous (column-like) structure with the column
diameter and inclination depending on the deposition angle. Polarimetric investigations
revealed that both in-plane and out-of-plane anisotropy was present, which is associated
with the columnar growth. The correlation between the PC manifestations and the
scanning electron microscopy results is analyzed. It was found that the tilt angle of
columns in obliquely deposited SiOx is smaller than that predicted by the “tangent rule”
and “cosine rule” models, and depends on the crystallographic orientation of Si substrate.
It is concluded that the proposed method is effective non-destructive express technique
for the structural characterization of obliquely deposited films.
Keywords: polarization conversion, ellipsometry, anisotropy, oblique deposition, silicon
oxide, nanostructure, microstructure.
Manuscript received 02.02.11; accepted for publication 14.09.11; published online 21.09.11.
1. Introduction
The microstructure of thin films is of great interest both
from scientific and practical points of view because of
many physical and chemical properties of films are
controlled by their microstructure [1, 2]. Very often thin
films exhibit columnar microstructure when deposited
by vapor condensation processes in vacuum [3-5]. It is
known [3-9] that formation of the columnar structures
depends on the material being evaporated, substrate type
and temperature, vapor pressure as well as the vapor
incidence angle α, i.e. the angle between film normal and
vapor deposition direction (obliqueness angle). The
columns tend to lean toward the incident flux with an
angle β relative to the surface normal (β < α).
SiOx films obtained by the oblique deposition of
the evaporated silicon monoxide (SiO) in vacuum also
form a structure with inclined columns [10]. Recently,
the method of porous light-emitting structure formation
using oblique deposition of SiO in vacuum was proposed
[11]. During high-temperature annealing of these films,
the thermally stimulated formation of Si nanoinclusions
(nc-Si) occurs in a restricted volume of the SiOx columns
thus forming the silicon-based light emitting nc-Si-SiOx
structures, in which Si nanoparticles (nc-Si) are
surrounded by porous oxide matrix (SiOx).
Study of specific features of both as-deposited and
thermally and/or chemically treated SiOx film is crucial
for the goal-directed control of luminescent
characteristics of the structures. Solution of this problem
requires the methods of a columnar microstructure
characterization (simple, express and non-destructive
ones are especially desirable). Structural anisotropy (the
shape anisotropy and the packing anisotropy) in the
films with oblique columnar structure seems to induce
strong anisotropy in their optical properties. This makes
it possible to consider polarimetric methods as feasible
effective instrument for characterization of these films.
In this paper, on the example of SiOx films, a
simple polarimetric method for the study of structural
© 2011, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
273
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2011. V. 14, N 3. P. 273-278.
anisotropy in obliquely deposited layers is proposed and
tested. To determine the characteristics of the possible
structural anisotropy, it was suggested to measure the so-
called cross-polarization or p-s polarization conversion
(PC) effect. The results obtained using the proposed
method are compared with the scanning electron
microscopy (SEM) results.
2. Experimental
The studied samples were fabricated by thermal
evaporation of 99.9% pure silicon monoxide SiO (Cerac
Inc.) in vacuum onto polished c-Si (111)
and c-Si(100) substrates oriented at the angles α = 0°,
60°, 75° between the normal to the substrate surface and
the direction to the evaporator. The substrate
temperature during deposition was 150 °C. Because of
additional oxidation by residual gases during
evaporation of SiO, the compositionally
nonstoichiometric SiO
( ) Pa1021 3−×−
x (x > 1) films were deposited in
the vacuum chamber. The deposition rate and the
thickness of the films being monitored in situ using the
KИT-1 quartz microbalance system.
The SiOx oblique deposited film (ODF) growth
morphology was visualized by ZEISS EVO 50XVP
scanning electron microscope. The geometrical thickness
of the films was also measured with MИИ-4
interferometric microscope. Multiangle ellipsometric
measurements have been performed to determine the
thickness and refractive index of the films. The
measurements were done using the PCSA null-type
ellipsometer (Feodosia, Ukraine)
equipped with He-Ne laser as a light source (λ =
632.8 nm). The same ellipsometer was used for the
investigation of PC in the films.
1-3M-ЛЭФ
3. Foundations of the proposed method
It is well known that for light reflection from an
isotropic film the p-s polarization uncoupling condition
is valid [12]:
Ep′ = rp Ep, Es′ = rs Es , (1)
where Ep and Es are the components of incident wave
(one is parallel to the incidence plane and another is
perpendicular to it). The corresponding components of
the waves reflected from the film are denoted as Ep′ and
Es′, respectively. In general, for anisotropic film the p-s
polarization uncoupling condition is broken and the
incident and reflected waves are related by 2×2
reflection matrix as follows [12-16]:
Ep'= rpp Ep + rps Es , (2)
Es′ = rsp Ep + rss Es ,
© 2011, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
where the subscripts “ps” and “sp” denote s-wave
converted to p-wave and p-wave converted to s-wave,
respectively (polarization conversion), whereas “pp” and
“ss” represent p-wave reflected as p-wave and s-wave
reflected as s-wave.
To obtain full information about optical (and thus
structural) anisotropy of ODFs from polarimetric
investigations, it needs, in general, to solve inverse
problem of ellipsometry in the framework at least
“biaxially anisotropic uniform layer” model with the use
of spectral and/or angular dependences of ellipsometric
parameters Δ and Ψ measured at various relative
orientation of light incidence plane and vapor deposition
plane (the plane containing both the substrate normal
and the vapor incidence vector is referred to as the
deposition plane). It is rather difficult task that can be
solved by numerical fitting the measured Δ and Ψ angles
data with an appropriate model [15, 16].
Based on above described general principles of PC
effect, we have realized a more simple method for the
analysis of optical anisotropy in ODFs which makes it
possible to obtain information about the structure of the
films, specifically, on such important parameter as
columns tilt angle β. This method explores the fact that
off-diagonal elements rps and rps are appreciably smaller
than diagonal elements rpp and rss [12-16]. As a result, in
general, in case of s(p)-linear polarized incident wave
the reflected wave will be elliptically polarized, but the
ellipse of polarization will be strongly elongated and its
major axis will have some small angle with the s(p)-
direction. The absolute value of this angle will be
proportional to ⎜rps / rss ⎜for s- or ⎜rsp / rpp ⎜ for p-
polarized incident wave.
At the transition to the isotropic situation, rps and
rsp diminish, and the relationship (1) is valid. The p-s
polarization uncoupling condition (1) is also valid for
some special cases of anisotropic media, precisely, when
one of the main axes of dielectric function tensor εik is
perpendicular to the incident plane. This is possible
when this axis is parallel to the plane of substrate
surface. If two principal axes of εik are parallel to the
sample surface and mutually perpendicular, and the third
axis is perpendicular to the first two axes, then rps and rps
will be zero precisely through the every 90° when the
substrate is rotated around the surface normal axis. For
example, for the Lengmuir-Blodgett films with a weak
in-plane anisotropy of the sample and with the third
principal axis being slightly (several degrees) tilted from
the surface normal, experimental dependences of
Re(rps /rpp) and Re(rps /rss) versus the azimuth angle Ω are
close to the cosine (sinusoidal) dependence with the
180° period [13].
From geometrical consideration one may assume
that in ODFs two principal axes of εik are located in the
vapor deposition plane (one of the axes coincides with
the longitudinal axis of the columns and the second one
is perpendicular to the first) and the third axis is
perpendicular to this plane. That is why, one could
expect that at low angles of column inclination rps and rsp
will be zero for the cases when the light incidence plane
will coincide with or perpendicular to the vapor
incidence plane, which is through, approximately, every
90°. For sufficiently inclined columns, rps and rsp will be
zero only for the case when the light incidence plane will
274
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2011. V. 14, N 3. P. 273-278.
coincide with the vapor incidence plane, which is
through every 180°. So, the simplest way to determine
the essential features of the anisotropy in ODFs is to
measure the angle between the main axis of polarization
ellipsoid for the reflected wave and s-direction of the
incident wave as a function of the azimuth angle Ω (Ω is
the angle between the laser beam incidence plane and
the vapor deposition plane). For this purpose, the
polarizer and the compensator of laser ellipsometer
are adjusted to obtain the s-polarization of
the laser beam projected on the sample (incidence angle
of the laser beam was φ
1-3M-ЛЭФ
0 = 45°). Samples were mounted
on the rotating stage of the ellipsometer, thus allowing a
complete 0°–360° variation of Ω (the value Ω ≡ 0°
corresponds to the situation when the laser beam
incidence plane coincides with the vapor deposition
plane, and the laser beam falls on the sample surface
from the same side as the vapor flux does). The sample
surface was accurately set normal to the rotation axis of
the stage.
Let us direct the s-polarized at isotropic or
uniaxially anisotropic sample with distinguished optical
axis perpendicular to its surface and pass the reflected
from such sample light through analyzer of ellipsometer.
At setting the analyzer in position at which it transmits
light of p-polarization (designate this position as Аs), the
light intensity, transmitted by the analyzer, will be zero
at any Ω. In other words, for these two types of samples
the reflected light will remain s-polarized at any Ω.
This result was obtained for reflection from the
monocrystalline silicon substrates and the substrates with
normally deposited SiOx films. But at the reflection from
the substrates with SiOx ODFs the p-s polarization
uncoupling was not observed, and as a result of PC effect
minimal intensity of the light transmitted by the analyzer
was at other position of analyzer (designate as Аmin). For
small values of rps / rss the angle of the rotation of the
analyzer (Аmin – Аs) is proportional to the rps / rss and
approximately equal to the angle θ between the main axis
of polarization ellipsoid for reflected wave and s-direction
of the incident wave (θ = Аmin – Аs). The angular
resolution of the instrument is 1′ for θ and 6′ for Ω.
4. Results and discussion
To estimate the thickness and refractive index of the
films, the inverse problem of ellipsometry was solved
for deposited SiOx films. By fitting the measured Ψ(φ0)
and Δ(φ0) angles data with “isotropic uniform layer” and
“uniaxial uniform layer” models, the thickness and
optical constants of the films were determined. The
Nelder-Meed method was used to minimize the
difference between experimental ellipsometric angles
Ψ(φ0) and Δ(φ0) and theoretical ones.
The solution of inverse problem of ellipsometry for
SiOx film deposited at α = 60° in the frameworks of both
isotropic and uniaxial anisotropic layer models gave the
values of the film thicknesses that are close to one
another and to the interferometric value. Within the
former n = 1.545, and within the latter the anisotropy is
rather small (no = 1.559, ne = 1.565). Results obtained
using uniaxial anisotropic layer model are indicative of
column-like porous microstructure in films with
preferential orientation of columns and pores along the
normal to substrate [17]. It is indirect evidence that in-
plane anisotropy of the sample is rather weak and the
third principal axis is slightly tilted from the surface
normal. The values of refractive index for this SiOx ODF
are sufficiently smaller than refractive index values of
normally deposited dense SiOx films (n ≈ 2.0).
Obviously, it is caused by higher porosity of obliquely
deposited SiOx films [11].
For the SiOx film deposited at α = 75°, the
considerable discordance between the models of
isotropic and uniaxially anisotropic layer takes place:
within the former n = 1.545, h = 668 nm and within the
latter nav = 1.423, h = 755 nm values are obtained. As
seen, the isotropic layer gives close n values for the
films deposited at both 60° and 75°. “Uniaxial
anisotropic layer” model gives much less n values for
the film deposited at 75°. It is more consistent with the
general expected trends of increased porosity with vapor
deposition angle (this tendency is also valid for SiOx
ODFs [10, 11]). Moreover, the h value obtained in
uniaxial anisotropic layer model is closer to the
interferometrically determined h value. Nevertheless the
use of this model is still inadequate approximation
because the sign of anisotropy depends on the
orientation of light incidence plane. These results of
ellipsometric modeling indicate that higher anisotropy
(connected, obviously, with more inclined columns)
takes place in the SiOx ODF deposited at α = 75° as
compared to the films deposited at α = 60°.
As was stated above, on the contrary to normally
deposited films, in oblique deposited films the
polarization conversion takes place. The θ value depends
on the orientation of light incidence plane relative to the
plane of vapor deposition (Ω). The dependences θ on Ω
obtained at rotation of the ellipsometer stage with SiOx
ODFs are shown in Figs 1 and 2.
Fig. 1 demonstrates this dependence for the SiOx
films deposited at α = 60° on c-Si substrate with (111)
orientation of its surface. For this film, the reflected light
remains s-polarized when Ω is close to 0°(360°), 90°,
180°, 270° (Fig. 1). For other values of Ω, the light is
elliptically polarized. The θ(Ω) dependence for this case is
close to the dependence θ(Ω) = Bsin(Ω/2), but there are
some deviations from the latest one – the absolute value of
θ(Ω) extrema in the first and fourth quadrants is somewhat
smaller as compared to the second and third ones. Such
character of the θ(Ω) dependence (with 180°-period and
some asymmetry in the extrema values) confirms that two
principal axes of εik tensor are in proximity to the plane of
film surface – one of them is nearly normal and other
nearly parallel to the direction of the projection of the
vapor-beam direction on the substrate surface. And the
third principal axis of εik is perpendicular to the substrate
surface or is somewhat deflected from the surface normal.
© 2011, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
275
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2011. V. 14, N 3. P. 273-278.
The experimental θ(Ω) dependence from Fig. 1 agrees in
general with the results of papers [13] as well as [18]
where the 180° azimuth period has been observed for
optical parameters characterizing PC in TiO2 films with
slightly inclined columns (β ≤ 20°). So, one may expect
that for the SiOx film deposited at α = 60° the β value is
close to 20°. This estimation don’t coincide with the
values predicted by the most used and recognized models
describing the relation between β and α [4, 19, 20]. The
tangent rule tan β = 0.5 tan α [4, 19] for α = 60° gives
β ≈ 41°, and the cosine rule sin (α − β) = (1 − cos α/2) [17]
for α = 60° gives β ≈ 45°.
Fig. 2 shows the dependence of θ on Ω for the SiOx
film deposited at α = 75°. The condition θ = 0 (Аmin = Аs)
is valid when Ω is close to 0°(360°), 25°, 180° and 335°.
Despite much more complicated form of the θ(Ω)
dependence for this sample there is some similarity with
the previous one. The transformation of θ(Ω)
dependence from Fig. 1 to Fig. 2 includes further
decrease of ⎜θmax(min)⎜ in the first and fourth quadrants as
well as narrowing these quadrants from Ω = [0° − 90°]
and Ω = [270° − 360°] to Ω = [0° − 25°] and Ω =
[335° − 360°], correspondingly. The second and third
quadrants have broadened at the expense of the first and
fourth quadrants, correspondingly. As a result, the period
of the θ(Ω) dependence in Fig. 2 is equal to 360°, and in
outline the dependence is close to the θ(Ω) = Bsin(Ω)
dependence which is presented by solid line in Fig. 2. In
this case, one or two of the principal axes of εik were
sufficiently deflected from the substrate surface and/or
substrate surface normal. It directly shows that more
inclined columns are formed in this film.
© 2011, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
SEM results confirm the conclusions made on the
basis of polarimetric results. The scanning electron
imaging of the SiOx film profiles demonstrates that the
films grow in columnar manner, the individual columns
run through the entire volume from the substrate plane to
the film surface. Besides, the oblique deposition leads to
the column inclination toward the substrate plane, the
columns being elongated in the vapour beam direction.
Fig. 3 shows the cross-sections of the obliquely
deposited at α = 60° (in the top panel) and α = 75° (in
the bottom panel) SiOx films. The β values for the SiOx
ODFs determined by scanning electron microscopy are
26–29° for α = 60°. These β values are significantly
smaller than those predicted by the tangent rule and the
cosine rule, but close to β values obtained in [18]. SEM
reveals more inclined nanocolumn structure of the SiOx
ODFs deposited at α = 75° as compared to the case
α = 60° (Fig. 3a and 3b). Determined by SEM β values
for the SiOx ODFs deposited at α = 75° were 34°–41° in
various points of the sample. So, they are also
significantly smaller than those predicted by the tangent
rule (gives β ≈ 62°) and the cosine rule (gives β ≈ 53°).
Results of Figs 1 to 3 indicate that the deviation of
the θ(Ω) experimental dependence from equation θ(Ω) =
Bsin(Ω/2) is more pronounced for the films deposited at
higher angles and, consequently, with more inclined
columns.
0 45 90 135 180 225 270 315 360
-60
-40
-20
0
20
40
60
θ,
m
in
Ω, degree
Fig. 1. Measured values of θ (crosses) as a function of the
sample azimuth Ω for the SiOx films deposited at α = 60° on c-
Si substrate with (111) crystallographic orientation. Solid curve
is the dependence θ(Ω) = Bsin(Ω / 2) with BB = –50'.
0 45 90 135 180 225 270 315 360
-60
-40
-20
0
20
40
60
θ,
m
in
Ω, degree
Fig. 2. θ(Ω) dependence for the SiOx films deposited at α = 75°
on c-Si substrate with (111) crystallographic orientation of
surface (crosses). Solid line – the dependence θ(Ω) = Bsin(Ω)
with BB = +65'.
Recently, a semi-empirical analytical model for the
β versus α relationship has been proposed [8]. It uses one
input parameter, the fan angle, and fits experimental data
better than the tangent and cosine rules. Using this
model, we have estimated the fan angle in our physical
vapor condensation of SiOx films. The obtained value of
the fan angle is 62-68° and may be partially caused by
collisions of the evaporated species in vapor flux. Such
collisions will cause the loss of directionality of the
evaporated particles in their way to the substrate. In
recent theoretical investigation [7] by solving the Monte
Carlo ballistic model, using diverse calculated incident
angle distribution functions in various conditions, it has
been shown that the loss of directionality leads to the
column tilt angle decrease (it corresponds to the increase
of fan angle in terms of the model [8]).
The above described polarimetric technique for the
analysis of the ODFs structure has been used to
276
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2011. V. 14, N 3. P. 273-278.
investigate SiOx films deposited on the monocrystalline
silicon substrates with different crystalline orientation of
the surface (Fig. 4). These samples were annealed in
vacuum at 975 °C. Fig. 4 demonstrates that deviation of
the θ(Ω) experimental dependence from θ(Ω) =
Bsin(Ω/2) is a little more pronounced for the film on c-
Si(111) substrate. It means that the column tilt angle β is
greater in the film on c-Si(111) substrate. A greater tilt
angle of columns resulted in greater porosity of these
films, but the difference in column tilt angle and,
consequently, in porosity is very small. Nevertheless, it
was found that the nc-Si-SiOx films, deposited on c-
Si(111), are dissolved by HF vapors more rapidly than
the films on c-Si(100).
Fig. 3. Scanning electron micrograph images for SiOx samples
prepared by oblique deposition at 60° (a) and 75° (b) off-
normal on c-Si substrate with (111) surface orientation.
0 45 90 135 180 225 270 315 360
-1000
-750
-500
-250
0
250
500
750
1000
θ,
m
in
Ω, degree
Fig. 4. θ(Ω) dependence for the SiOx films deposited at α = 75°
on c-Si substrate with (100) (circles) and (111) (crosses)
orientation of substrate surface, then annealed at 975 °C in
vacuum.
550 600 650 700 750 800 850
0
6
12
18
24
I P
L,
a.
u.
λ, nm
Fig. 5. Spectral dependence of PL for the SiOx films deposited
at α = 75° on c-Si substrate with (100) (circles) and (111)
(crosses) orientation of substrate surface, then annealed at
975 °C in vacuum and HF vapor treated for 1 min.
To control the photoluminescence (PL) intensity and
PL peak position of light emitting nc-Si-SiOx structures,
the annealed SiOx films are treated by HF vapor [21]. As a
result of HF vapor treatment, considerable PL intensity
growth (near 200 times of magnitude) and blueshift of PL
peak position are observed. It is suggested that the
evolution of the PL spectra in HF vapor-treated samples
can be attributed to selective-etching-induced decrease in
Si nanoparticle dimensions and to passivation of Si
dangling bonds (that are nonradiative recombination trap
states) by hydrogen and oxygen.
Fig. 5 shows the difference in PL spectra of HF
treated nc-Si-SiOx structures deposited on c-Si substrates
with different orientation. We suppose that this
difference is caused by the difference in column tilt
angle in the annealed SiOx films. Since the films with
more inclined columns are more porous (structure
deposited on c-Si (111) substrate), they are more
susceptible to chemical vapor treatments because the
dissolving vapors more easily penetrate into these films.
It produces more complete passivation of nonradiative
traps and higher PL intensity. More effective vapor
treatment causes higher oxidation of the nc-Si surface,
more expressed decrease in nc-Si sizes, and some
blueshift of the PL spectrum.
These results show an important role of substrate
surface in formation of the nanocolumn structure of
ODFs. Further comprehensive study of this effect may
make significant contribution in elucidation of a
structure formation mechanism in SiOx ODFs and
nc-Si-SiOx structures formed on their base.
From Fig. 4, it could be concluded that a difference
in column tilt angle for the films on c-Si(100) and c-
Si(111) substrates is not significant. But the difference in
the dissolution rate in HF vapors is large. That is why,
fixation of small structural differences in SiOx ODFs is
very important, and the proposed polarimetric method
makes it with high sensitivity. At the same time, fixation
© 2011, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
277
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2011. V. 14, N 3. P. 273-278.
of this small difference can be problematic with SEM.
The reason of that – destructive nature of SEM as
technique for analysis of column inclination in ODFs. In
order to measure the actual column inclination, one must
fracture the sample in the deposition plane. But, SEM is
sensitive to misalignment between the deposition plane
and the fracture plane, as well as polar misalignment.
Obviously, just these errors are the reason of the some
scattering of β value at the SEM measurement in various
points of our samples. Moreover, the columns located
near the fracture site have slightly different inclinations
due to edge irregularities, introducing a new source of
error [16]. On the contrary, the proposed simple
polarimetric technique is very sensitive to the
differences in the microstructure of ODFs and, in
addition, poses the advantage of non-destructivity.
5. Conclusions
In summary, we have presented a specific simple optical
approach for the investigation of obliquely deposited
films. This technique is based on the modulation of the
normalized off-diagonal terms of the Jones reflection
matrix, induced by the rotation of the anisotropic sample.
The study of polarization conversion is realized by means
of conventional null-ellipsometer, and it reveals the type
of optical anisotropy caused by columnar structure of the
films and makes it possible to estimate the tilt angle of
columns. We apply this method to the characterization of
SiOx films and nc-Si-SiOx light emitting nanostructures,
deposited on silicon substrates. Structural difference
between films simultaneously deposited on Si substrates
with (100) and (111) crystallographic orientations of
surface has been established. The technique may be
utilized for characterization of obliquely deposited thin
films during their fabrication and processing.
References
1. A.-L. Barabasi and H.E. Stanley, Surface Growth.
Cambridge University Press, Cambridge, England,
1996.
2. P. Meakin, Fractals, Scaling and Growth Far from
Equilibrium. Cambridge University Press, New
York, 1998.
3. N.G. Nachodkin and A.I. Shaldervan, Effect of
vapour incidence angles on profile and properties of
condensed films // Thin Solid Films, 10(1), p. 109-
122 (1972).
4. A.G. Dirks and H.J. Leamy, Columnar
microstructure in vapor deposited thin films // Thin
Solid Films, 47(3), p. 219-233 (1977).
5. R. Messier, A.P. Giri and R.A. Roy, Revised struc-
ture zone model for thin film physical structures // J.
Vac. Sci. Technol. A, 2(2), p. 500-503 (1984).
6. H. van Kranenberg and C. Lodder, Tailoring growth
and local composition by oblique-incidence
deposition: a review and new experimental data //
Mater. Sci. Eng. R, 11(7), p. 295-354 (1994).
7. J.M. García-Martín, R. Alvarez, P. Romero-Gómez,
A. Cebollada and A. Palmero, Tilt angle control of
nanocolumns grown by glancing angle sputtering at
variable argon pressures // Appl. Phys. Lett. 97(17),
173103–173103-3 (2010).
8. B. Tanto, G. Ten Eyck and T.M. Lu, A model for
column angle evolution during oblique angle
deposition // J. Appl. Phys. 108(2), 026107–026107-3
(2010).
9. M.V. Sopinskyy, V.I. Mynko, I.Z. Indutnyi, O.S.
Lytvyn and P.E. Shepeliavyi, Surface self-ordering
in obliquely deposited As2S3 films // Chalcogenide
Lett. 5(11), p. 239-247 (2008).
10. S.R. Kennedy and M. Brett, Porous broadband
antireflection coating by glancing angle deposition //
J. Appl. Opt. 42(22), p. 4573-4579 (2003).
11. I.Z. Indutnyy, I.Yu. Maidanchuk, V.I. Min’ko,
P.E. Shepeliavyi and V.A. Dan’ko, Visible
photoluminescence from annealed porous SiOx films
// J. Optoelectron. and Adv. Mater. 7(3), p. 1231-
1236 (2005).
12. R.M.A. Azzam and N.M. Bashara, Ellipsometry and
Polarized Light. Amsterdam, North-Holland, 1986.
13. B. Lecourt, D. Blaudez and J.-M. Turlet, Specific
approach of generalized ellipsometry for the
determination of weak in-plane anisotropy:
application to Langmuir–Blodgett ultrathin films // J.
Opt. Soc. Amer. A, 15(10), p. 2769-2782 (1998).
14. Yi-Jun Jen and Cheng-Yu Peng, Narrow-band and
broad-band polarization conversion reflection filters
// Appl. Phys. Lett. 89(4), 041128–041128-3 (2006).
15. W. Xu, L.T. Wood and T.D. Golding, An
ellipsometric method for the determination of the
dielectric tensor of an optically uniaxial material
suited for in-situ measurements // Thin Solid Films,
384(2), p. 276-281 (2001).
16. G. Beydaghyan, C. Buzea, Y. Cui, C. Elliott and
K. Robbie, Ex situ ellipsometric investigation of
nanocolumns inclination angle // Appl. Phys. Lett.
87(15), 153103–153103-3 (2005).
17. L.A. Golovan’, P.K. Kashkarov and
V.Yu. Timoshenko, Form birefringence in porous
semiconductors and dielectrics: a review //
Crystallography Repts. 52(4), p. 672-685 (2007).
18. M. Schubert, B. Rheinländer, J.A. Woollam, B. Johs
and C.M. Herzinger, Extension of rotating-analyzer
ellipsometry to generalized ellipsometry: determina-
tion of the dielectric function tensor from uniaxial
TiO2 // J. Opt. Soc. Amer. A, 13(4), p. 875-883 (1996).
19. J.M. Nieuwenhuizen and H.B. Haanstra,
Microfractography of thin films // Philips Tech. Rev.
27, p. 87-91 (1966).
20. R.N. Tait, T. Smy and M.J. Brett, Modelling and
characterization of columnar growth in evaporated
films // Thin Solid Films, 226(2), p. 196-201 (1993).
21. V.A. Dan’ko, V.Ya. Bratus’, I.Z. Indutnyi,
I.P. Lisovskyy, S.O. Zlobin, K.V. Michailovska and
P.E. Shepeliavyi, Control of photoluminescence
spectra of porous nc-Si-SiOx structures by vapor
treatment // Semiconductor Physics, Quantum
Electronics & Optoelectronics, 13(3), (2010).
© 2011, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
278
|