Materials Today: Proceedings xxx (xxxx) xxx
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Influence of organosulphur additives on autocatalytic copper thin film
deposition
P. Balaramesh a,⇑, S. Jayalakshmi b, S. Absara Fdo a, V. Anitha c, P. Venkatesh b
a
Department of Chemistry, R.M.K. Engineering College, Kavaraipettai, Chennai 601206, India
Department of Chemistry, Pachaiyappa’s College, Chennai 600030, India
c
Department of Chemistry, Vellammal Engineering College, Surapet, Chennai 600066, India
b
a r t i c l e
i n f o
Article history:
Available online xxxx
Keywords:
Glyoxylic acid
Methanesulphonic acid
Organosulphur
Surface morphology
Xylitol
a b s t r a c t
This article reports the effect of organosulphur additives such as 2-Mercaptobenzothiazole and 2Benzothiophene on electroless copper bath. Trace quantity of biodegradable methanesulphonic
Bronsted acid was used to develop an ecofriendly electroless bath. Toxic free natural polyhydroxylic complexing agent, Xylitol, Glyoxylic acid, an excellent reducing agent and to control free metal ion concentration, pH modifier, Potassium hydroxide were used. 1 ppm and 10 ppm concentration of
organosulphur additives were optimized and analyzed at 45 °C at a pH of 13.0 ± 0.25. Inhibiting and
accelerating effect of organosulphur additives depends upon throwing power, thickness uniformity, surface tension, grain structure control and deposit characteristics. The physical parameters were calculated
by weight gain and gravimetric methods. Corrosion kinetics and electrochemical properties of ecofriendly
electroless bath were analyzed by cyclic voltammetry and the Tafel plot. Surface morphology and structural property of pure copper deposits were investigated by scanning electron microscopy and atomic
force microscopic methods.
Ó 2021 Elsevier Ltd. All rights reserved.
Selection and peer-review under responsibility of the scientific committee of the International Web Conference on Advanced Materials Science and Engineering.
1. Introduction
Metal coating process started from 18th century with just polishing and silvering plates but did not gain attention from
researchers and scientists [1]. Since 19th century, scientific
description with various metal ions like Ni2+ were reduced by
hypophosphite ions and well-known works with silvering method
for fabricating mirrors commenced [2]. The official pioneer work of
the deposition process improved with copper on glass containing
copper and formaldehyde, followed by silvering of glass [3]. In
20th century, this method got noticed and created interest
amongst researchers and produced first patent in the process of
producing metallic deposits. After the Second World War, there
have been significant advances in all traditional surface engineering techniques such as electroplating, hot dip coatings, anodizing,
organic paints, and plastics etc. [4,5].
⇑ Corresponding author at: Department of Chemistry, R.M.K. Engineering College,
Kavaraipettai, Chennai 601206, India.
E-mail address: pbr.sh@rmkec.ac.in (P. Balaramesh).
The controlled electroless plating process was accidently discovered by A.R. Brenner and G.E. Riddell in 1946 [6], when they
tried to electroplate Ni–W alloy on the inner side of a steel tube
using a citrate bath. They modified the plating bath using several
reducing agents including sodium hypophosphite [7]. To their surprise, they found that the exterior surface of the steel tube was also
coated, and this had accounted for the increased current efficiency
of 120% of the theoretical value. After careful analysis, they concluded that, the coating formed on the exterior of the steel tube
might have been formed by chemical reduction, induced by
hypophosphite.
Later, Narcus et al. [8] reported and established an optimum
plating condition, which was the first commercial application
and theoretical basis of electroless copper deposition. In this process the chemical reducing agent provides electrons, necessary to
produce a metallic deposit rather than external electric current.
Hence the process was called ‘chemical plating’ [9]. Based on its
analogy with the electroplating process, William Blum [10] coined
the term ‘Electroless plating’ for this process.
The future of electroless plating seemed gloomy in the 21st century, but with increasing demands in electronics, space, defence,
https://doi.org/10.1016/j.matpr.2021.04.212
2214-7853/Ó 2021 Elsevier Ltd. All rights reserved.
Selection and peer-review under responsibility of the scientific committee of the International Web Conference on Advanced Materials Science and Engineering.
Please cite this article as: P. Balaramesh, S. Jayalakshmi, S. Absara Fdo et al., Influence of organosulphur additives on autocatalytic copper thin film deposition, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2021.04.212
P. Balaramesh, S. Jayalakshmi, S. Absara Fdo et al.
Materials Today: Proceedings xxx (xxxx) xxx
2.2. Formula for rate of copper deposition
and other industries it turned profitable [11–13]. The commercial
applications of deposition processes have increased in printed circuit boards and electronics industries, integrated circuit, metallization of carbon nanotubes, metals on polymers, lightweight metal
composites, ultra-large-scale integration (ULSI), through-hole connections for printed wiring boards and flexible circuits, electromagnetic interference (EMI), microcircuits used in radar and
space vehicles [14–18].
The major constituents of electroless plating process are metal
ions, reducing agent, complexing agent, and pH adjusting agent.
Since, electroless plating baths undergo spontaneous decomposition, some additives are also added. These improve the stability
of the bath, metal binding property and alter physical and mechanical properties of the deposits in the solution. Hetero atoms like
sulphur, nitrogen and oxygen containing aromatic organic stabilizers show better surface affinity, thickness uniformity, grain structure control, with deposit brightness and hardness than the
aliphatic compounds [19,20]. Natural polyhydroxylic compound,
xylitol could provide alternatives to EDTA currently used as complexing agents in electroless plating baths. They form very stable
complexes with copper (II) ions in alkaline solution. KOH was used
as pH adjuster to increase the solubility of the by-products during
electroless copper deposition. Organic stabilizers are found to
greatly stabilize the bath and extend its life.
In this work, we prepared biodegradable electroless methanesulphonate bath at optimized pH of 13.0 ± 0.25 at 45 °C. Organosulphur compounds like 2-Mercaptobenzothaizole (2-MBT), and 2Benzothiophene (2-BTP) were used as the stabilizers with 1 ppm
and 10 ppm concentration. 2-MBT is used in many fields due to
its strong adhesion capability and corrosion inhibiting property.
It is also used as a vulcanization agent. 2-BTP forms stable complex
and is important in the field of pharmacy.
Novelty of this work is the use of biodegradable Bronsted acid
Methanesulphonic acid (MSA) as the bath liquid. MSA’s superiority
over other bath liquids arises from its excellent metal salt solubility, stability, biodegradability, excellent conductivity, and ease of
effluent treatment. Another attractive feature of this bath liquid
is that, the bath can be operated at room temperature. Addition
of small amounts of MSA has been reported to produce uniform
and high-quality coatings. However, literature survey shows that,
not much work has been carried out to understand and optimize
bath conditions. This work fills the gap through this study and
the effect of MSA on bath deposition efficiency has been established [21,22].
In other coating process the article or samples are measured in
micro scale. But electroless coated articles are exceptionally
smooth, compact and can also achieve nanoscale deposition
[23,24]. Moreover, electroless plating process has better physical,
electrochemical, and structural properties [25,26].
The rate of deposition (T) was calculated using the following
relation:
lm
¼ Thickness Deposition time
Rate ofdeposition
h
ð1Þ
where W is the mass of the deposit (g), d is the density of the film
material (g/cm3); ‘A’ is the area of the film coated (cm3) and‘t’ is the
coating duration (h).
Rate of the electroless copper deposit was calculated using the
following equation
Deposition rate
lm
W 104
T¼
h
dAt
ð2Þ
2.3. Calculation for thickness of copper deposits
After electroless plating, the panel was washed, rinsed, dried,
and weighed (w1). The electroless copper coating was dissolved
in 10–20% HNO3 solution. Then the panel was washed, rinsed,
dried, and weighed (w2). The actual weight of the deposit was calculated from the difference in weight before and after plating (w1w2). From the weight of the deposit, total plated area and density
of the copper, thickness was calculated as follows
Thickness ðlmÞ ¼
W 104 60
AD
ð3Þ
where,
W = (w1-w2) = Weight of deposit (g)
w1 = Weight after plating (g)
w2 = Weight after stripping (g)
A = Total plated area of the substrate (cm3)
D = Density of the copper (g/cm3)
2.4. Formula for activation energy by Arrhenius equation (AE)
The activation energy is inversely proportional to the rate of
deposition. It was calculated by the following Arrhenius equation.
Ea ¼ slope 2:303 R
ð4Þ
3. Techniques and characterization
3.1. Surface morphology – scanning electron microscope (SEM)
SEM is one of the most widely used techniques used in characterization of nanomaterials and nanostructures and is also used for
the examination and analysis of the micro structural characteristics of solid objects. It is an improved model of an electron microscope. SEM is also capable of examining objects in a wide range of
magnifications. It is used to produce an enlarged threedimensional image of a specimen of exceedingly small size even
in the order of Å.
2. Methodology
2.1. Eco-friendly chemical bath preparation
An environment friendly electrolyte was prepared by using analytical grade chemicals. The electroless deposition of copper was
performed using methanesulphonate, glyoxylic acid, potassium
hydroxide (to vary the pH of the bath) and organic stabilizers
(1 ppm and 10 ppm). The electroless deposition was performed
on an epoxy sheet (2.0 2.0 0.1 cm) in a 100 ml beaker. Prior
to deposit, the substrate was rinsed with double distilled water
after polishing with fine grit paper. The effect of bath conditions
and various properties on plating deposition process was studied.
3.2. Nanostructure – atomic force microscope (AFM)
AFM is a part of the family of scanning probe microscope (SPM).
It shows high resolution type with demonstrated resolution of
fractions of a nanometer, 1000 times more than the optical diffraction limit. These microscopes work by measuring a property such
as height, optical absorption, with a probe or ‘tip’ placed remarkably close to the sample. Atomic force microscope (AFM) was used
to analyze the surface roughness of the Cu deposit.
2
Materials Today: Proceedings xxx (xxxx) xxx
P. Balaramesh, S. Jayalakshmi, S. Absara Fdo et al.
the corrosion potential. The reduction current can be obtained by
plotting the logarithms of current (log I) vs. potential and extrapolating the currents in the two Tafel regions. Knowing Icorr, the rate
of corrosion can be calculated in desired units by using Faraday’s
law. The modern techniques for measurement of corrosion rates
are based on the classical work of Stern and Geary.
3.3. Quality and quantity -cyclic voltammetry (CV)
Cyclic voltammetric curves were obtained using the standard
electrochemical analyzer. The copper methanesulphonate solution
was deaerated with nitrogen gas. The counter electrode was platinum wire and reference electrode was Ag/AgCl with saturated
KCl solution. The voltammograms were recorded at room temperature 28 ± 2 °C in 0.1 M Na2SO4 supporting electrolyte. Standard
glassy carbon electrode was used as working electrode and the
voltammograms were recorded in the range from 1.2 to +0.5 V
at a potential scanning rate of 50 mVs1.
4. Results and discussion
The acceleration and inhibiting property of the stabilizers was
confirmed with the deposition rate of xylitol plain bath. Low deposition rate indicate the inhibiting nature and enhanced deposition
rate indicates the accelerating action of the stabilizers. Using
weight gain and gravimetric method, the thickness of the copper
deposition can be calculated. Similarly, activation energy also can
be calculate by using Arrhenius equation. The Table 1 and Fig. 1
show that, by the addition of 1 ppm of 2-MBT, all the physical
properties have been lowered and further, an increase in the concentration of 2-MBT to 10 ppm resulted in a decreased deposition
rate value than the xylitol plain bath. So, 2-MBT stabilizer acts as
3.4. DC electrochemical monitoring technique - Tafel polarization (TP)
The polarization curves for the anodic and cathodic reactions
are obtained by applying potentials against SCE, far away from
Table 1
Physical properties of xylitol plain bath with stabilizers (1 ppm and 10 ppm) on
electroless copper bath.
Xylitol PB with
Organosulphur
Stabilizers
Xylitol PB
2-MBT
1 ppm
10 ppm
2-BTP
1 ppm
10 ppm
Physical properties
Deposition Rate
(lm/h)
Thickness
(lm)
Activation Energy
(kJ/mol)
3.02
2.76
2.72
3.52
3.43
181.2
165.6
163.2
211.2
205.8
70.4
62.8
61.0
77.6
74.8
Table 2
Surface properties of xylitol plain bath with stabilizers (1 ppm and 10 ppm) on
electroless copper bath.
Xylitol PB with
Organosulphur
Stabilizers
Xylitol PB
2-MBT
2-BTP
1 ppm
10 ppm
1 ppm
10 ppm
Surface properties
SEM - Shape
AFM – Roughness
Value (nm)
Rocks
Grains
Pyramid
Flower
Honeycomb
216
138
156
122
128
Fig. 2. AFM images of copper deposits on methanesulphonate bath (a) topography
of copper deposits (b) 3-D image and (c) surface area; (1a, 1b, 1c) xylitol PB, (2a, 2b,
2c), 2-MBT (1 ppm), (3a, 3b, 3c) 2-MBT (10 ppm), (4a, 4b, 4c) 2-BTP (1 ppm), and
(5a, 5b, 5c), 2-BTP (10 ppm).
Fig. 1. SEM images of copper deposits on methanesulphonate bath with (a) 2000
and (b) 5000 magnification, (1) xylitol plain bath, (2) 2-MBT (1 ppm), (3) 2-MBT
(10 ppm) (4) 2-BTP (1 ppm), and (5) 2-BTP (10 ppm).
3
P. Balaramesh, S. Jayalakshmi, S. Absara Fdo et al.
Materials Today: Proceedings xxx (xxxx) xxx
the inhibitor. 2-BTP act as the accelerator and the results indicate
that the electroless bath containing 1 ppm concentration of stabilizers, resulted in elevated the physical properties.
The surface morphology of copper deposits was studied by the
SEM and AFM analysis. Different and interesting shapes, such as
grains, pyramid, flower, and honeycomb were observed by these
methods. Topography of the copper deposits, 3D- image and surface area were observed by the AFM method. Table 2 and Fig. 2
show that, 2-BTP produces interesting shapes and better roughness
values than 2-MBT. Moreover, the result show that the bath containing 1 ppm of 2-MBT and 2-BPT produced the copper deposits
with lower roughness value than the xylitol plain bath.
The electrochemical property of an ecofriendly electroless bath
solution was observed by cyclic voltammetry and Tafel polarization studies. Based on low and high anodic peak current, anodic
peak potential values, broad and sharp peak appearances, the role
of stabilizer is decided. From Table 3, Fig. 3, and Fig. 4, the inhibiting property of 2-MBT was confirmed by the decreased Epa-1 value
and the increased anodic peak current value, than the plain bath.
Electroless copper bath with 1 ppm 2-BTP produce better potential,
current and deposition rate than the 2-MBT, that evident of the
accelerating potential of 2-BTP.
Table 3
Electrochemical properties of xylitol plain bath with stabilizers (1 ppm and 10 ppm)
on electroless copper bath.
Two different ecofriendly electroless bath were prepared by
using organosulphur stabilizers and conclusion are as following:
Xylitol PB with
Organosulphur
Stabilizers
Xylitol PB
2-MBT
1 ppm
10 ppm
2-BTP
1 ppm
10 ppm
5. Conclusion
The deposition rate, thickness and activation energy indicate
that, 2-MBT stabilizer acted as an inhibitor and 2-BTP acted as
an accelerator.
An interesting surface morphological phenomenon was
observed when those two stabilizers were used in xylitol containing methanesulphonate bath. The roughness values were
observed at below 200, when compared with plain bath value.
The anodic peak potential (Epa-value) and anodic peak current
value (Ipa-value) were observed by cyclic voltammetry studies.
Icorr and deposition rate value were calculated from the Tafel
plot. The electrochemical properties of the stabilizers were
boosted in the bath containing 1 ppm concentration than
10 ppm concentration.
The physical and electrochemical data clearly indicates that, the
xylitol bath with organosulphur stabilizers 2-MBT and 2-BTP produced copper deposits, which are compact, finer, smoother, and
more shiny than the deposits resulted from the xylitol plain bath.
Electrochemical properties
CV
Tafel
Epa-1
(mV)
Ipa-1
(mA)
Icorr
(mA)
Deposition
Rate (lm/h)
0.2210
0.2399
0.2621
0.2032
0.2186
3.054
3.445
3.318
5.167
3.489
50.64
46.64
42.18
72.92
65.31
0.670
0.542
0.486
0.992
0.816
CRediT authorship contribution statement
P. Balaramesh: Conceptualization, Methodology, Writing original draft, Formal analysis, Project administration. S. Jayalakshmi: Visualization, Investigation, Data curation, Interpretation.
S. Absara Fdo: Data curation, Formal analysis. V. Anitha: Formal
analysis, Data curation, Interpretation. P. Venkatesh: Validation,
Resources, Supervision.
Fig. 3. Cyclic voltammogram for electroless copper methanesulphonate (a) xylitol
plain bath, (b) 2-MBT (1 ppm); (c) 2-MBT (10 ppm), (d) 2-BTP (1 ppm), (e) 2-BTP
(10 ppm).
Declaration of Competing Interest
-0.6
The authors declare that they have no known competing financial interests or personal relationships that could have appeared
to influence the work reported in this paper.
-0.8
-1.0
-1.2
-1.8
xylitol PB (1)
xylitol+2-MBT+1 ppm (2)
xylitol+2-MBT+10 ppm (3)
xylitol+2-BTP+1 ppm (4)
xylitol+ 2-BTP+10 ppm (5)
-2.0
(1)
Current / A
-1.4
-1.6
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Fig. 4. Tafel polarization curve for copper deposits with electroless copper
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