ABSTRACT Tin oxide has multiple technological applications including Li-ion batteries, gas sensors, optoelectronic devices, transparent conductors and solar cells. In this study tin dioxide (SnO 2 ) thin films were deposited on glass substrates by RF sputtering process in the oxygen (O 2 ) and argon (Ar) plasma medium. The deposition of the thin SnO 2 films was carried out by RF sputtering from SnO 2 targets. Before deposition the system was evacuated to 10 -4 torr vacuum level and backfilled with Ar. The deposition of the nano structured thin SnO 2 films have been performed at different gas pressures. The deposition of the SnO 2 was both carried out at different pure argon gas pressures and argon/oxygen mediums with varying oxygen partial pressures. The effect of argon and argon/oxygen partial gas pressures on the grain structure and film thickness were analyzed in the resultant thin films. The deposited thin films both on glass and stainless steel substrates were characterized with scanning electron microscopy (SEM), X-ray diffractometry equipped with multi purpose attachment. The grain size of the deposited layer was determined by X-ray analysis. The Atomic Force Microscopy (AFM) technique was also conducted on the some selected coatings to reveal grain structure and growth behaviors

Ahmet Alp

Deniz Gultekin

Hatem Akbulut

Mehmet Oguz Guler

Mirac Alaf

CiteSeerX

DownloaTHE EFFECT OF PRESSURE ON THE MICROSTRUCTURAL BEHAVIOUR ON SnO2 
THIN FILMS DEPOSITED BY RF SPUTTERING 
 
 
Mehmet Oguz Guler, Mirac Alaf, Deniz Gultekin, Hatem Akbulut, Ahmet Alp 
Sakarya University Engineering Faculty, Department of Metallurgical & Materials Engineering, Esentepe Campus, 
54187, Sakarya/Turkey, guler@sakarya.edu.tr  
 
 
 
Proceedings of MN2008 
2nd International Conference and Exhibition on  Multifunctional Nanocomposites and Nanomaterials 
January 11-13, 2008, Sharm El Sheikh, Egypt 
MN2008-47071 
 
 
ABSTRACT 
Tin oxide has multiple technological applications including 
Li-ion batteries, gas sensors, optoelectronic devices, 
transparent conductors and solar cells. In this study tin dioxide 
(SnO2) thin films were deposited on glass substrates by RF 
sputtering process in the oxygen (O2) and argon (Ar) plasma 
medium. The deposition of the thin SnO2 films was carried out 
by RF sputtering from SnO2 targets. Before deposition the 
system was evacuated to 10-4 torr vacuum level and backfilled 
with Ar. The deposition of the nano structured thin SnO2 films 
have been performed at different gas pressures. The deposition 
of the SnO2 was both carried out at different pure argon gas 
pressures and argon/oxygen mediums with varying oxygen 
partial pressures. The effect of argon and argon/oxygen partial 
gas pressures on the grain structure and film thickness were 
analyzed in the resultant thin films. The deposited thin films 
both on glass and stainless steel substrates were characterized 
with scanning electron microscopy (SEM), X-ray 
diffractometry equipped with multi purpose attachment. The 
grain size of the deposited layer was determined by X-ray 
analysis. The Atomic Force Microscopy (AFM) technique was 
also conducted on the some selected coatings to reveal grain 
structure and growth behaviors. 
 
Keywords: RF sputtering, SnO2, gas pressure, nano grain. 
 
 
ded From: https://proceedings.asmedigitalcollection.asme.org on 06/29/2019 Terms o1. INTRODUCTION 
 In the recent years tin oxide has become one of the most 
important industrial materials in the semiconductor market. 
Semiconducting properties of doped and undoped tin oxide 
films have been used in the fabrication of the transparent 
conducting films [1-3], architectural glasses because of their 
high reflectivity of infrared light [4] and protective coatings 
because of their high resistance to corrosion and wear [5]. Tin 
oxide has also been used for gas sensors for the inflammable 
gases [6]. 
 
The production of the tin oxide films can be obtained using 
several deposition techniques including evaporation [7], 
reactive sputtering from a pure metallic tin target [8], sol-gel 
[16] and chemical vapor deposition [9] and spray pyrolysis 
[10]. The properties of the manufactured SnO2 films are highly 
dependant on the grain structure that can be changed due to the 
manufacturing techniques. 
 
Tin oxide is an n-type semiconductor having an optical 
band gap of 3.6 eV in polycrystalline form [11]. Tin oxide films 
crystallize in tetragonal rutile structure (Casiterite) under 
optimum deposition conditions [12]. Tin oxide films have a 
molecular weight of 150.71 atomic mass unit (AMU) with 6.95 
gr/cm3 specific gravity. The melting and the boiling point of the 
SnO2 films are 1127 °C and 1800-1900 °C.  
 
In this study tin oxide films have been deposited onto 
microscope glass slides by RF sputtering at room temperature. 
RF sputtering has been employed due to the poor electrical 
conductivity of the SnO2 target. In addition, the microstructural 
variations have been examined by SEM, XRD and AFM 
techniques. 
 
1 Copyright © 2008 by ASME 
f Use: http://www.asme.org/about-asme/terms-of-use
Do2. EXPERIMENTAL DETAILS 
The RF sputtering process has been performed in a 
commercial coating system equipped with RF and DC 
Magnetron sputtering. The system is also capable of producing 
films with thermal evaporation. High purity SnO2 (99.999 %) 
targets having 2” diameter, Ar (99.9999 %) and O2 (99.999 %) 
have been used in the processes.  
 
Before starting the coating processes the UHV chamber 
has been evacuated to 3.37 x 10-6 torr and then the chamber has 
been filled with Ar and Ar + O2 gas mixtures for coating 
processes untill 1.37 x 10-2 torr. RF powers of 147, 160 and 
212 W have been employed for the coatings at 100 % Ar, 95% 
Ar + 5% O2 and 90% Ar + 10% O2 atmospheres. 
 
Before starting the processes the microscope glass slides 
have been heat treated to 600 °C by increasing the temperature 
incrementally (6 °C/min). Such a heat treatment is needed for 
microscope glass slides because of a hygienic PTFE layer. This 
layer should have to be removed before starting the coating 
processes. The heat treatment processes have been performed 
using Nabertherm ash furnace. After the heat treatment process 
the microscope glass slides have been cleaned using distilled 
water, ammonia and hydrogen peroxide (5:1:1). They were then 
rinsed carefully using methanol, acetone and distilled water 
carefully. 
 
The effects of the different RF powers and oxygen 
pressures on the microstructure of the fabricated films have 
been studied. The crystallite sizes of the coatings have been 
calculated by using XRD (Rigaku D/MAX 2000 with multi 
purpose attachment). The formation of the grains has been 
examined by using SEM (Jeol 6060 LV). AFM studies have 
also been performed on several selected samples in order to 
evaluate the grain structure and growth behavior. 
 
3. RESULTS AND DISCUSSIONS 
Figure 1, 2 and 3 show the XRD spectra of the SnO2 films 
prepared by RF magnetron and RF reactive magnetron 
sputtering at various oxygen partial pressures (0%, 5%, 10% 
Oxygen and the rest is argon) using 147 W, 160 W and 212 W 
RF power respectively. As could be seen from the XRD spectra 
under pure Ar atmosphere, the crystalline growth has been 
developed mostly in the (110) plane. However, introducing 
oxygen into the UHV chamber results in the nano-crystalline 
SnO2 films to grow in the (101) and (211) planes. The intensity 
of the crystals on the (211) plane has been increased rapidly 
which proves that the preferred texture orientation has become 
evident on the (211) plane. 
 
14
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20
40
60
80
100
120
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10 20 30 40 50 60 70 80 90
2θ
In
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 (A
rb
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 U
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 - 
C
%100 Ar
%95 Ar + %5 O2
%90 Ar + %10 O2
■ SnO2 (110)
♦ SnO2 (101)
▲SnO2 (211)
In
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 (A
rb
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 U
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 - 
C
PS
)
 
Figure 1. XRD spectra of the tin films fabricated by using 
7 W RF power under various oxygen partial pressures (100% 
rgon, 95% Argon + 5% Oxygen, 90% Argon + 10% Oxygen). 
0
20
40
60
80
100
120
140
160
10 20 30 40 50 60 70 80 90
2θ
In
te
ns
ity
 (A
rb
ita
ry
 U
ni
ts
 - 
C
%95 Ar+%5 O2
%90 Ar+%10 O2
%100 Ar
■ SnO2 (110)
♦ SnO2 (101)
▲SnO2 (211)
In
te
ns
ity
 (A
rb
ita
ry
 U
ni
ts
 - 
C
PS
)
 
Figure 2. XRD spectra of the tin films fabricated by using 
0 W RF power under various oxygen partial pressures (100% 
rgon, 95% Argon + 5% Oxygen, 90% Argon + 10% Oxygen). 
0
20
40
60
80
100
120
140
160
180
200
10 20 30 40 50 60 70 80 90
2θ
In
te
ns
ity
 (A
rb
ita
ry
 U
ni
ts
 - 
C
%90 Ar +%10 O2 
%95 Ar + %5 O2 
%100 Ar
■ SnO2 (110)
♦ SnO2 (101)
▲SnO2 (211)
In
te
ns
ity
 (A
rb
ita
ry
 U
ni
ts
 - 
C
PS
)
 
Figure 3. XRD spectra of the tin films fabricated by using 
2 W RF power under various oxygen partial pressures (100% 
rgon, 95% Argon + 5% Oxygen, 90%Argon + 10% Oxygen). 
 
The crystalline sizes of the fabricated films have also been 
amined by using the Scherer formula [12]; 
 
θ
λ
BCos
D 9.0=                  (1) 
 
where D is the mean grain size of the fabricated films, λ is 
e wavelength of the X-ray that is 0,154 nm, θ is the Bragg 
ffraction angle and B is the FWHM of the fabricated thin 
ms in radians. 
 
2 Copyright © 2008 by ASME 
 Use: http://www.asme.org/about-asme/terms-of-use
Downloa8
9
10
11
12
1 2 3
Partial Pressure (Argon and Oxygen)
M
ea
n 
G
ra
in
 S
iz
e 
(n
110 101 211
%100 Argon %95 Argon + %5 Oxygen %90 Argon + %10 Oxygen
M
ea
n 
G
ra
in
 S
iz
e 
(n
m
)
 
Figure 4. Mean grain size alterations in the various 
directions due to the partial pressure of the oxygen in 147 W of 
RF power. 
 
8
9
10
11
12
13
14
0,5 1,5 2,5 3,5
Partial Pressure (Argon + Oxygen)
M
ea
n 
G
ra
in
 S
iz
e 
(n
110 101 211
%95 Argon + %5 Oxygen %90 Argon + %10 Oxygen%100 Argon
M
ea
n 
G
ra
in
 S
iz
e 
(n
m
)
 
Figure 5. Mean grain size alterations in the directions due 
to the partial pressure of the oxygen in 160 W RF power. 
 
10,8
11,2
11,6
12
12,4
12,8
0,5 1,5 2,5
Partial Pressure (Argon + Oxygen)
M
ea
n 
G
ra
in
 S
iz
e 
(
3,5
n
110 101 211
%95 Argon + %5 Oxygen %90 Argon + %10 Oxygen%100 Argon
M
ea
n 
G
ra
in
 S
iz
e 
(n
m
)
 
Figure 6. Mean grain size alterations in the directions due 
to the partial pressure of the oxygen in 212 W RF power. 
 
As could be seen from figures 4, 5 and 6 that the mean 
grain sizes of the nano crystalline tin films have been varied 
from 9 nm to 12 nm in size. The crystalline sizes become larger 
with the increasing RF power and partial oxygen pressure. 
 
Surface morphology of the manufactured films has also 
been examined by SEM and AFM analysis. Figures 7, 8 and 9 
show the surface morphology of the manufactured tin films 
under different oxygen partial pressures by using 147 W RF 
power. Surface roughness and porosity have been increased by 
increasing the oxygen partial pressure. 
14
14
14 
ded From: https://proceedings.asmedigitalcollection.asme.org on 06/29/2019 Terms of Use 
Figure 7. SEM analysis of the tin films fabricated by using 
7 W RF power under pure argon atmosphere (x20 000). 
 
Figure 8. SEM analysis of the tin films fabricated by using 
7 W RF power under 5% oxygen partial pressure (x20 000). 
 
Figure 9. SEM analysis of the tin films fabricated by using 
7 W RF power under 10% oxygen partial pressure (x20 000). 
 
3 Copyright © 2008 by ASME 
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Figure 10. SEM analysis of the tin films fabricated by 
using 212 W RF power under pure argon atmosphere (x30 
000). 
 
Figure 11. SEM analysis of the tin films fabricated by 
using 212 W RF power under 5% oxygen partial pressure (x20 
000). 
 
Figure 12. SEM analysis of the tin films fabricated by 
using 212 W RF power under 10% oxygen partial pressure 
(x20 000). 
in
fro
un
un
ha
fig
th
th
tin
ch
ro
su
ap
po
ro
or 
Downloaded From: https://proceedings.asmedigitalcollection.asme.org on 06/29/2019 Terms of Use: 
The porosity and roughness were all increased with the 
creasing power and partial oxygen pressures as could be seen 
m Fig. 10, Fig. 11 and Fig. 12. 
 
Figure 13. AFM analysis of the tin films manufactured 
der 5% Oxygen partial pressure by using 147 W RF power. 
 
Figure 14. AFM analysis of the tin films manufactured 
der 5% Oxygen partial pressure by using 160 W RF power. 
 
AFM analysis has also proved that increasing the power 
s also increased the roughness of the surfaces as shown in 
ures 13 and 14. 
 
Nano crystalline tin oxide films have been fabricated and 
e effects of the oxygen and RF power have been examined in 
is study. The results have shown that it is possible to produce 
 oxide films with desired orientation and microstructure. The 
aracteristics such as thickness, grain size, orientation and 
ughness could be easily regulated by changing the parameters 
ch as RF power and oxygen partial pressure due to 
plication area. The results have shown that increasing the RF 
wer and oxygen partial pressure increases the grain size, 
ughness and porosity of the film. In addition, the preferred 
ientation is also changed.  4 Copyright © 2008 by ASME 
 http://www.asme.org/about-asme/terms-of-use
DoACKNOWLEDGMENTS 
This work is supported by the Scientific and Technical 
Research council of Turkey (TUBITAK) under the contract 
number 105T260. The authors thank the TUBITAK TBAG 
workers for their kind supports. 
REFERENCES 
[1] Z. M. Jarzebski and J. P. Marton, “Physical properties of 
SnO2 materials” Journal of Electrochemical Society, 123 (7), 
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[2] D. Das and R. Banerjee, “Properties of electron-beam-
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[3] H. S. Randhawa and M. D. Mattehews, “SnO2 films 
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[4] G. Frank and E. Kauer, “Transparent heat-reflecting 
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wnloaded From: https://proceedings.asmedigitalcollection.asme.org on 06/29/2019 Terms of U[7] D. W. Lane and J. A. Coath, “Optical properties and 
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[8] L. I. Popova and M. G. Michailov, “Structure and 
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THE EFFECT OF PRESSURE ON THE MICROSTRUCTURAL BEHAVIOUR ON SnO 2 THIN FILMS DEPOSITED BY RF SPUTTERING

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THE EFFECT OF PRESSURE ON THE MICROSTRUCTURAL BEHAVIOUR ON SnO 2 THIN FILMS DEPOSITED BY RF SPUTTERING

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