2005 NDL Nano-Device Conference
The Vacuum Annealing of ITO and ITO/Cu Transparent Conductive Films
in Hydrogen Atmosphere
Tien-Chai Lin ,
Shang-Chou Chang ,
Chun-Ming Yang , Chin-Fu Chiu ,Yung-Kuang Wu , Chien-Chang Lu , Yeu-To Hsin
Department of Electrical Engineering, Kun Shan University of Technology, Tainan, Taiwan
Abstract
in vacuum furnace with hydrogen atmosphere. The
A copper film was deposited on ITO glass substrates
energy transport into ITO and ITO/Cu films in heat
to form ITO/Cu film using direct current magnetron
treatment process could induce the atomic vibration and
sputtering in room temperature and with argon gas. The
diffusion to arrange lattice structure for well crystalline.
ITO and ITO/Cu films were heated in vacuum and in
The crystal structure, resistivity and transmittance could
hydrogen atmosphere to develop the relation of
be studied and discussed with temperature effect at as
electronic
deposit and annealing samples in this study.
and
optical
properties
with
annealing
temperature. The results of ITO films shown the
resistivity was reduced from 6.2*10-4Ω-cm to 2.7*10-4Ω
2. Experimental
-cm in annealing process and the average optical
The substrate was used in ITO glass which was
transmittance was beyond 90%. The ITO/Cu shown a
supported by industrial company with 0.63mm thickness
very low value of resistivity in as deposit was 2.8*10 Ω
of glass coated with 150nm ITO film. The glass materials
-cm and the transmittance was between 58~72%.
were made in soda-lime with a dimension of 1.5*5 cm2.
Keywords: indium tin oxidation, annealing, sputtering,
A 99.99% purity copper was used as target materials. A
resistivity
ITO glass substrate was cleaned in standard wet process
-4
and dried in nitrogen. The first sputtering step was
1. Introduction
pumping to 10-6torr background pressure. A DC power
In the decade, the flat panel display was a well
was connected to cathode and the substrate holder was
development, the TN and STN LCD was the early
rotated for thickness uniformity. The deposition time and
products, nowadays more people were interested in the
pressure were 2min and 5 mtorr, respectively. After Cu
TFT-LCD and PDP. In the future, the OLED maybe play
deposition, the ITO and ITO/Cu substrate was stayed on
an important role in display industry. Whatever the
vacuum chamber with 100sccm H2 for annealing. The
transparent conductivity films
was necessary for
pressure was keep at 20 torr and the treatment time was
photo-electro industry, the film has to be a low resistivity,
20 min. The temperature was changed from 100oC to
high absorption in utra violent light region and high
500oC at every step of 100oC. The crystalline structure,
optical transmittance in visible light region, the ITO film
electrical properties and transmittance were investigated
is popular as an electrode in display application[1-3].
by XRD, a four probe measurement and optical spectrum
This oxide of ITO with a n type semi conductive
analysis, respectively. According to analysis datum, the
properties, its conductivity mechanisms are free electron
ITO and ITO/Cu films were discussed with annealing
carrier and oxygen vacancy. In this study, the Cu film
affected the electro-photo characteristics.
coated on ITO glass is for the purpose of improving ITO
conductivity because the Cu resistivity is a very low
3. Results and discussion
value of 1.67*10 -cm it is roughly only one percentage
3-1 crystalline structure
of ITO. At annealing treatment the specimen was located
Fig.1 shows the XRD spectrum of ITO with various
-6
2005 NDL Nano-Device Conference
annealing temperature. The ITO film is almost
phenomenon results in high energy atom moving toward
amorphous or nano-crystalline at as deposit and the films
the substrate and strike the substrate to transfer a kinetic
are crystallized while the annealing temperature is
energy into thermal energy. The energy exchange let the
o
o
reached at 100 C or 300 C. The prefer orientation of
ITO get some thermal energy in accorded with annealing
heated samples is tended to (222) plane. Fig.2 shows the
effect therefore, the ITO is crystallized at as deposit.
ITO/Cu
The Cu in ITO/Cu films at beyond 100 oC annealing
XRD
spectrum
with
different
annealing
temperature from 100 oC to 500 oC.
treatment are found some crystal XRD peaks such as
(111) plane. It is easy to understand the thermal energy in
ITO (222)
Intensity(arb. unit)
heating process support atoms to diffuse and stack, and
ITO (440) (a) 300oC
reduce deposition defects to format a more perfect
structure in result of decreasing the total energy.
(b) 100oC
3-2 Electrical properties
The resistivity of ITO film dependent on annealing
temperature is shown in Fig.3. The resistivity at as
(c) as-deposit
0
20
40
2
60
80
deposit is 6.2*10-4 Ω-cm and slightly increases with
temperature raised, till 200oC the resistivity have a
Fig.1 XRD spectrum of ITO with various annealing
highest value of 6.7*10-4Ω-cm then low down. At 500oC
temperature
annealing, the best conductivity can be found and its
Cu (111)
ITO (222)
ITO (211)
value is 2.7*10-4Ω-cm.
(a) 500oC
8
(b) 400oC
6
Resistivity (*10-4-cm)
Intensity(arb. unit)
ITO(440)
(c) 300oC
4
2
(d) 200oC
0
(e) 100oC
0
100
200
300
Temperature (oC)
400
500
Fig.3 The resistivity of ITO film dependent on
(f) as-deposit
annealing temperature
0
Fig.2
20
ITO/Cu
XRD
40
2
60
spectrum
with
80
different
annealing temperature from 100 oC to 500 oC
According to H. Morikawa and M. Fujita[4]
research of ITO annealing, they showed the ITO film
crystallizing temperature is about 165oC and the
At as deposit Fig.2(f), the copper without any
resistivity increase when the film structure change from
diffraction peaks shows a amorphous structure but the
amorphous to crystalline then low down at temperature
ITO(222) and (440) are observed it indicates the
still increased. The result is as well as our experimental
amorphous ITO film are crystallized at after Cu
of
deposited process. While the copper obtains a kinetic
diffusion and rearrangement to format crystallized
energy transported from argon colliding target, the
structure. Because very small crystal grain generate in
Fig.1. The thermal energy induces the atomic
2005 NDL Nano-Device Conference
initial crystallization step, the resistivity increase in
flows from the lower resistance Cu surface but not in
attribution of an amount of grain boundary as an electron
ITO film. The total resistance calculate as follow:
carrier transport barrier. Over 200 oC, the ITO film
1
constructs completely crystallized and grain size raise in
RTotal

1
1

.............(1)
RCu R ITO
dependent on increasing annealing temperature. The total
The ITO/Cu in annealing process, there are two effects to
grain boundary reduced, the stacking defect disappeared
control film conductivity, one is pure ITO discussed in
and more indium atoms into substitution site during grain
previous statement and another is copper film. The Cu
growth result in the carrier have less barriers in transport
with a high diffusion coefficient migrates quickly to ITO
and the conductivity increase obviously especially at
film at heat process. The copper is formed Cu++ ion and
500oC. In general, hydrogen is a reductive gas as
indium is generated In+3. When Cu diffuse to ITO film
annealing atmosphere can product an oxygen vacancy for
during thermal process it will substitute indium site.
oxide materials.
According to different valance of Cu++ and In+3, the
But nitrogen is an inert gas as a
protective gas, it is not able to
create vacancies of
substitution
site
product
holes
otherwise
the
annealed ITO. Previous researcher published[3,5,6] that
recombination appears with electron of n-type ITO. This
carrier concentration increase in H2
atmosphere
phenomenon reduces the conductivity of ITO and the
They shown the
thickness of Cu layer become thinner, therefore, the
conductivity raised is attributed in H2 reacting with tin
resistivity increase dependence on temperature increased.
annealing by Hall measurement.
oxide to reduction oxide become OH bond and leave an
oxygen vacancy.
The annealing effect of ITO/Cu with
resistivity is shown in Fig.4 which curve tendence is
similar with Fig.3 of pure ITO.
5
Resistivity (*10-4-cm)
4
3
Fig.5 A current model of ITO/Cu to formation of
2
parallel resistance circuit
1
3-3 Optical properties
0
0
100
200
300
Temperature (oC)
400
500
Fig.6 shows the transmittance of ITO film depend on the
Fig.4 The annealing effect of ITO/Cu with resistivity
annealing temperature detected by optical spectrum
analysis measurement. The average transmittance is
The resistivity at as deposit have very low value of
carried out 550nm wavelength. The transmittance is not
2.7*10 Ω -cm but it increase at 100 C and 200 C
obviously change in whole annealing temperature and as
annealing, beyond 300oC, the resistivity slowly reduce to
deposit which always keeps at approximate 90%. The
2.8*10 Ω-cm at 500 C. The resistivity of ITO/Cu is less
transmittance
than a half of ITO, whatever this two layer design is
temperature is shown in Fig.7 which is lower than pure
effective for promoted conductivity.
ITO. The transmittance of as deposit is 58% and increase
Fig.5 shows a current model of ITO/Cu to formation of
at a range of 62~72% with annealing temperature raised.
-4
-4
o
o
o
parallel resistance circuit. It indicates amount of current
change
of
ITO/Cu
with
various
2005 NDL Nano-Device Conference
100
beyond this temperature the structure of ITO/Cu is
without identified change. For the resistivity analysis, the
Transmittance (%)
90
results show the resistivity at as deposit is 6.2*10-4Ω-cm
80
and slightly increases with temperature raised, till 200 oC
the resistivity have a highest value of 6.7*10 -4Ω-cm then
70
low down. At 500oC annealing, the best conductivity can
60
be found and its value is 2.7*10-4Ω-cm. The ITO/Cu
shows the resistivity at as deposit have very low value of
50
0
100
200
300
Temperature (oC)
400
500
2.7*10-4 Ω -cm but it increase at 100oC and 200oC
Fig.6 The transmittance of ITO film depend on the
annealing, beyond 300oC, the resistivity slowly reduce to
annealing temperature
2.8*10-4 Ω -cm at 500oC.
The ITO is not obvious
change in transmittance with temperature and the
100
transmittance is roughly at the range of 90%. The
Transmittance (%)
90
ITO/Cu with low transmittance, the range is 58%~72%.
80
Reference
70
1. W.F. Wu, B.S. Chion , ” Properties of
Radio-Frequency Magnetron Sputtered ITO Films
60
without In-situ Substrate Heating and Post Deposition
50
Annealing”,Thin Solid Films, 247(1994)201
0
100
200
300
Temperature (oC)
400
500
2. T.C Gorjanc, D. Leong, C. Py, D. Roth,”Room
Fig.7 The transmittance change of ITO/Cu with various
temperature deposition of ITO using r.f. magnetron
temperature
sputtering” , Thin Solid Film, 413 (2002) 181-185
3. M. J. Morgan, Y. H. Aliyu, R. W. Bunce,
Although ITO/Cu have high conductivity the
A. Salehi,”
Annealing Effect on Opto-Electronic Properties of
transmittance is very low. The copper is a colorful metal
Sputtered and Thermal Evaporated Indium-Tin-Oxide
with a high absorption in visual wavelength therefore the
Film”, Thin Solid Films, 312（1998）268-272。
transmittance is strongly depend on the copper thickness.
4. H. Morikawa, M. Fujita, ”Crystallization and electrical
Whatever the ITO/Cu has very low resistivity in all
property change on the annealing of amorphous
annealing process it is a more potential for special
indium-oxide and indium-tin-oxide thin films”, Thin
display application.
Solid Films 359 (2000) 61-67
5. S.K. Park, J. I. Han, W. K. Kim, M. G.
4. Conclusion
Kwak, ”Deposition of indium-tin-oxide films on
The ITO glass substrate is an amorphous or nano
polymer substrates for application in plastic-based flat
grain structure, after annealing, it crystallizes beyond
o
100 C with a (220) orientated prefer. While copper
panel displays”,
Thin Solid Film, 397 (2001)49-55
6. K.H. Choi , J.Y. Kim , Y.S. Lee , H.J. Kim ,
coated on ITO glass formatted ITO/Cu provide a
“ITO/Ag/ITO multilayer films for the application of a
deposition heating for ITO
very low resistance transparent electrode” Thin Solid
in the result of ITO
crystallized at as deposited. The Cu is amorphous at as
o
deposit and crystallizes after heat treatment at 100 C
Films,
341(1999) 152-155