Indian Journal of Pure & Applied Physics
Vol. 46, March 2008, pp. 198-203
Growth and characterization of copper, indium and copper-indium alloy films
non-aqueous method of electrodeposition
S R Kumar*, B Prajapati†, S K Tiwari & V K Tiwari
Department of Applied Sciences & Humanities, National Institute of Foundry & Forge Technology, Ranchi 834 003
†
Department of Physics, Gossner College, Ranchi 834 001
*E-mail:srkumar20052923@rediffmail.com
Received 26 October 2006; revised 16 August 2007; accepted 14 January 2008
A new non-aqueous method for electrodeposition of copper, indium and copper indium alloy films, ethylene glycol has
been used as the solvent which is non-toxic and non-hazard bath. All the source materials are readily soluble in this bath and
they have higher working temperature (≥160°C). The copper films prepared in ethylene glycol based bath are preferred
(111) oriented with grains well connected to each other indicates the epitaxial growth. The indium film has been observed in
semi-molten state with intense (101) reflection. The Cu-In alloy film prepares at −1.1 V (Pt) is copper rich but the ratio
tends to be1.0 in the bulk of the film. Multiphase deposits are observed with grains which are spherical and well connected
to each other. The resistivity and carrier concentration of the as-deposited copper and copper indium alloy films are found to
be 0.2 Ω-cm, 9.9×1015 per cm3 and 2.5 Ω-cm and 5.5×1017 per cm3, respectively. The as-deposited films are found to be
resistive but the resistance decreases when the films are annealed at moderate temperature.
Keywords: Non-aqueous medium, Electrodeposition, Cathodic polarization, Stoichiometry, Survey scans, Sputtering
1 Introduction
Non-aqueous electrodeposition of semiconductors,
metal alloys has become a growing field of scientific
and technological interest. The metals, metal alloys
and semiconductors electrodeposited from aprotic
bath are expected to solve several engineering
problems. We mention here few important
applications. The task of electroplating ternary and
more complex semiconductors becomes increasingly
difficult in aqueous medium. In the electrodeposition
of copper indium selenide from aqueous bath, the
components viz. copper, indium and selenium exhibit
widely differing electrodeposition potentials. Thus,
the growth of stoichiometry CuInSe2 films has not
been possible1-5.
Hence, it is decided to study the deposition of
individual metals and characterize their properties
employing ethylene glycol as solvent. This work was
further extended to co-deposit Cu-In alloy films as
well. Such an approach should be advantageous in
terms of more effective and easier control over the
binary alloy composition and hence, that of the
CuInSe2 films eventually. Growth of CuInSe2 films
from a copper indium precursor has been followed by
earlier researchers also6-9; these baths are not very
suitable as copper and indium electrodeposition
potentials differ widely. One can express the
electrodeposition potential using the Nernst equation
as follows10:
(a) For copper deposition
Cu2+ + 2e < :::::> Cu
ECu < ::::> [E0 Cu+ (RT/ZF) In (aCu 2++/aCu)]
= 0.0295log aCu 2+
…(1)
(b) For indium deposition
In3+ + 3e < ::::> In
EIn < ::::> Eo1n + (RT/ZF) In (aIn3+/aIn)
= + 0.0197 logaIn3+
…(2)
where E refers to the electrode potentials with respect
to a normal hydrogen scale and a to the activities of
the ionic species. From Eqs (1) and (2), it is obvious
that the electrodeposition of Cu-In alloy in aqueous
medium is difficult as the corresponding standard
potentials (E0) differ by about 1.2V.
2 Experimental Details
Copper plating was carried out by dissolving AR
grade 2.9×10−3 M cupric chloride, 8.5×l0−3 M
ethylene diamine tetra acetic acid (EDTA), 1.5×I0−2 M
KI and 8.2×10−3 M triethanol amine (TEA) in 40 ml
of ethylene glycol. The bath was then allowed to age
199
KUMAR et al.: GROWTH AND CHARACTERIZATION OF FILMS
for some time. The electroplating bath for indium was
prepared by dissolving AR grade 9.08×10−3 M indium
chloride in ethylene glycol. To this bath, potassium
iodide, sodium citrate and triehanol amine were added
in the molar concentrations. Electroplating bath for
copper indium alloy was prepared by dissolving
9.08×l0−3 M indium trichloride, 2.9×10−3 M cupric
chloride together with KI, sodium citrate and TEA.
All reagents are AR grade. The electrodeposition
matrix was held at a constant temperature of 160°C
for several hours. This stabilization treatment was
necessary to obtain a uniform deposit composition.
Electrodeposition matrix of 40 ml was transferred
to a pre-dried corning glass beaker. Three electrode
geometry was employed during deposition with
polished nickel/molybdenum cathode, a graphite
counter electrode of dimension 4 cm2 and platinum
wire quasi-reference electrode. For corrosion
resistance of copper deposition steel, cathode was
used keeping the other electrode same. The reference
electrode was kept in a closed proximity to the
working electrode to minimize the electrolyte ohmic
drops. Suitable rigid supports were also provided to
ensure parallelism between the working and the
counter electrode.
Steady state cathodic polarisation characteristic of
the electroplating bath were plotted by scanning the
working electrode potential in an increasingly
cathodic direction with the help of an EG and G
potentiostat (Model 362). The stability of the bath
over a wide range of temperature and potential was
also verified prior to the experiments. On termination
of the electrodepositon routine, the samples were
quickly removed from the cell and dipped in boiling
distilled water for 10 min to ensure that any residual
electrolyte on the deposit surface is removed. The
samples were subsequently cleaned in a jet of distilled
water.
The composition of the alloy film was analyzed
using an ESCALAB mark II X-ray photo electron
spectrograph (VG Scientific, England). XPS analysis
were performed using an AlKα (hν=1486.6eV) source
and a concentric hemispherical analyser at resolution
of 0.8 eV.All the measured binding energies were
referred to the Au4 f7/2 peak located at 83.8 ± 0.1 eV.
An argon ion gun operating at 4 kV and 10 μA was
used for cleaning and profiling the films. Element
identities were established first by a survey scan.
Accurate compositional analysis was subsequently
carried out by repeatedly scanning the peaks over a
narrow energy range. The In 3d5/2, Cu 2P3/2, 0 Is and
C Is peaks were used for the determination of the
compositions by measuring the corresponding peak
areas and the element sensitivity factor using the
following relationship11.
Cx =
I x Sx
×100
Σ(l x / S x )
where Ix is the intensity of the peak (area under the
curve) for element x and Sx the sensitivity factor.
The electrodeposit structures were analysed using a
Phillips diffractometer model PW 1050/25 and Cu Kα
radiation. A Jeol scanning electron microscope (JSM
35CF) operating at 20 kV and normal incidence was
used to obtain the surface morphology of the deposits.
3 Results and Discussion
Figure 1(a) shows the cathodic polarisation
characteristics of the bath comprising 40 ml ethylene
glycol along with mill molar concentration of CuCl2,
EDTA and KI. As the deposition potential increases,
the current does not increase but at −0.2V (Pt) the
deposition current starts and it increases linearly.
Between the potential −0.75 V (Pt) to −1.0V (Pt)
current density slightly saturates and then again rises.
In this plateau range the deposition rate becomes
constant. On analyzing the deposition range, it is
Fig. 1 — Cathodic polarisation characteristic of ethylene glycol
alongwith (a) 2.9×10−3 M CuCl2 1.5×10−2 M KI, 1.7×10−2M
Na-citrate and 8. 2×10−3 M TEA (b) 9.8×10−3 M InCI3, 1.5×10−2
M KI and 8.2×10−3 M TEA (c) 2.9×I0−3 M CuCl2, 9.8×10−3 M
InCl3, 1.5×10−2 M KI, 1.7×10−2 M Na-citrate acid 8.2×10−3 M
TEA
INDIAN J PURE & APPL PHYS, VOL 46, MARCH 2008
observed, good deposition of Cu at −1.0V (Pt). Figure
1(b) shows the cathodic polarization characteristic of
40 ml ethylene glycol along with 9.08×10−3 M InCI3,
1.5×10−2 M KI, 8.2×10−3 M TEA and 1.7×10−2M Nacitrate. As the deposition potential increases, the
current does not increase but at −0.2V (Pt) the
deposition current starts and it increases linearly. The
rate of deposition becomes constant between the
potential range 0.5V (Pt) to −0.9V (Pt). At a
deposition potential of −1.0V (Pt), a uniform and
good deposition is observed. Figure 1(c) shows the
cathodic polarization characteristics of 40 ml ethylene
glycol alongwith 2.9×10−3M CuCI2, 1.5×10−2 M KI,
9.08×10−3 M InCI3, 8.2×10−3 M TEA and 1.7×10−2 M
Na-citrate. When the deposition potential increases,
the current does not rise but at a potential of −0.2V
(Pt) the current rises linearly. The initial rise in
current indicates the deposition of copper. As the
deposition potential increases further the current rises
but between potentials 0.6V (Pt) −1.0V (Pt) the
current saturates which indicates the constant rate of
deposition. Beyond −1.0 V (Pt) again a cathodic
process starts which indicate the deposition of indium.
It is observed that between the potential from −1.0 V
(Pt) to −1.2 V (Pt) co-deposition of both the elements
take place. Best deposition is observed at a potential
of −1.1 V (Pt).
In the electrodeposition process, polycrystalline
deposits take place. In case of polycrystalline
deposits, however, epitaxy is difficult although certain
preferred orientation can be seen. The XRD analysis
of copper films electrodeposited by us indicated that
the films are strongly oriented in (111) direction. The
XRD spectrum of a typical film is shown in Fig. 2(a).
Apart from the (111) and (200) peaks of nickel
which was used as the substrate. The surface
morphology of the as-deposited copper films is shown
in Fig. 3. A uniform distribution of the deposit is
evidenced from the SEM examination. Also no
evidence of cracking could be observed in our films
even after prolonged storage which indicates the
absence of any significant inclusion or stress in the
films.
The XRD spectra of indium film electroplated at
−1.0 V (Pt) is shown in Figure 2(b). An intense (101)
reflection of indium, some weak reflections from
(002, 100, 200) planes of indium were also detected.
These results indicate that the electroplated films
contain a preferred (101) orientation of the indium
metal. The evidence of oxidation of the
200
electrodeposited indium was also obtained as the
XRD spectra revealed peaks of (222), (332) and (600)
reflections of In203. The 2θ and d values
corresponding to all their peaks compared well with
the ASTM file (5-0642, 6-0416) as summarized in
Table 1. The SEM examination of the electroplated
indium indicated a molten deposit. The result is
Fig. 2 — (a) XRD spectra of a typical copper film electroplated at
−1.0 V (Pt), (b) XRD spectra of a typical indium film
electroplated at-1.0V (Pt) and (c) XRD spectra of as-deposited
Cu-In thin films electroplated at −1.1 V (Pt)
Fig. 3 — Scanning electron micrographs of a copper film
deposited at −1.0 V (Pt)
KUMAR et al.: GROWTH AND CHARACTERIZATION OF FILMS
201
Table 1 — Values of 2θ, d, relative peak height and possible crystal in the phases electrodeposited indium film in nonaqueous medium
2θ
30.63
32.84
36.21
39.04
41.54
44.37
51.69
54.36
56.43
Observed values
dÅ
2.91
2.72
2.47
2.30
2.17
2.03
1.76
1.68
1.62
Relative peak
height
2θ
d A0
156
1697
169
207
117
1498
1689
132
45
30.56
32.95
36.31
39.15
41.82
44.48
51.82
54.34
56.56
2.92
2.71
2.47
2.29
2.15
2.03
1.76
1.68
1.62
Standard values
Relative peak
height
100
21
36
—
—
—
—
12
Crystal phase &
Miller planes
In203(222)
In (101)
In (002)
1n (100)
In203(332)
Ni(111)
Ni(200)
1n203 (600)
In (200)
shown in Fig. 4, where the droplet like features
correspond to the electrodeposited indium. The
melting point of indium is 156°C. Since the bath
temperature employed in our case was higher (l60°C)
the indium deposit is expected to be in molten state
which condensed later on when the deposit was
removed from the bath.
Figure 2(c) shows the XRD spectra of the Cu-In
alloy film electroplated at-1.1 V (Pt). The intensity of
the (101) peak of indium is very prompt whereas the
intensity of Cu7In4 alloy is very small. These trends
indicate that the deposition at −1.1 V (Pt) favours
indium deposition with a preferred (101) orientation
whereas the Cu7In4 is less favoured. The morphology
of the film deposited at −1. 1 V (Pt) was examined
using scanning electron microscope and the result is
shown in Fig. 5. The polycrystalline nature of the
deposit can easily be seen in the Fig. 5. The grain size
and the deposit distribution were also fairly uniform
although some bigger surface particles were also seen
in the film.
It is possible to control the relative composition of
Cu and In in the electrodeposits by selecting a suitable
deposition potential. To ascertain the composition of
the film and chemical phases present we carried out
depth profiling experiments using survey as well as
narrow scan XPS spectra12. The XPS survey scans of
the film deposited at-1.1 V (Pt) obtained in the as
deposited is shown in Fig. 6. In all cases, peaks
corresponding to Cu, In, O and C were detected .The
depth profile of a typical Cu-In film deposited at −1.1
V (Pt) is shown in Figure 7. The copper and indium
concentration in this film changed continuously
indicating that these films are multiphase. The ratio of
copper and indium becomes equal to 1 after 30
minutes of sputtering.
Fig. 4 — Scanning electron micrographs of an indium film
deposited at −1. 0 V (Pt)
Fig. 5 — Surface topology of a typical Cu-In film
deposited at −1.1 V (Pt)
INDIAN J PURE & APPL PHYS, VOL 46, MARCH 2008
The variations in the photoelectron binding energy
of the elements with sputtering duration provide
information on the existence of their chemical
environment. Figures 8 and 9 show the narrow scan
XPS spectra of copper 2p3/2 and In 3d5/2 peaks after
202
various sputtering duration. The corresponding
binding energies are presented in Table 2. For the
films deposited at 1.1 V (Pt), the copper 2p3/2 binding
energy continuously changed with sputtering time
while the indium 3d5/2 binding energy, after 30 s of
sputtering remained practically invariant. From these
results, it appears that the electrode position is,
generally, yields a multiphase alloy consisting of the
free elements as well as oxides.
The resistivity of the thin film is calculated using
the formula:
ρ0 = (V/I) × 2 π S
Fig. 6 — XPS survey spectrum of the as received Cu-In film
electroplated at −1.1 V (Pt)
Fig. 8 — Comparison of narrow scan peaks of Cu 2P 3/2 peaks at
various sputtering duration for a Cu-In film electroplated at −1.1
V(Pt)
Table 2 — Comparison of the binding energies of different elements detected after various sputtering duration for Cu-In alloy film
deposited at −1.1 V (Pt)
Fig. 7 — Depth profile of the Cu-In film electroplated
at −1.1V (Pt)
Elements
0 min
sputter
30 sec.
sputter
2 min
sputter
5 min
sputter
10 min
sputter
20 min
sputter
30 min
sputter
Cu2p3/2
In3d5/2
O1s
C1s
932.5
444.7
530.0
285.1
932.7
444.4
529.0
284.9
932.8
444.4
285.0
933.0
443.5
529.5
286.0
933.0
443.5
529.5
285.0
932.5
443.4
529.7
284.0
932.8
443.4
529.9
284.0
203
KUMAR et al.: GROWTH AND CHARACTERIZATION OF FILMS
field, respectively. The observed carrier concentration
is in good agreement with the polycrystalline
materials.
4 Conclusions
It can be concluded that using the non-aqueous
bath, we can develop copper film at −1.0V (Pt),
indium film at −1.0V (Pt) and copper indium alloy
film at −1.1 V (Pt). The XRD and SEM results, thus,
clearly indicate that the non-aqueous bath employed
by us for the electrodeposition of copper can prove
useful in growing epitaxial copper films. This is a
useful result since epitaxial films can find
technological applications. In the case of Cu-In alloy,
a polycrystalline deposits are observed but grains are
well connected with each other. No effect of charging
are observed and average grain size is observed to be
0.5 μm. XPS analysis clearly indicate the ratio of
copper to indium is 1.0 in the bulk of the film but at
the surface, it is copper rich.
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Fig. 9 — Comparison of narrow scan peaks of In 3d5/2 peaks
of various sputtering duration for Cu-In film electroplated
at −1.1 V(Pt)
where ρ0 is the resistivity of the material (Ω-cm); V
the applied voltage (m V); I the applied current (mA);
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film is 2.5 Ω-cm which is high. The Hall voltage and
carrier concentration of the same film are observed to
be 0.2 mV and 5.5×1017/cm3 at 1250 Gauss magnetic
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