-
-0 wr7%
METALLIZATION OF POLYPYRROLE FILMS PART II: ELECTRODEPOSITION OF
COPPER PbF
ABSTRACT
Maria Hepel, Yi-Ming Chen and Laura Adams Department of
Chemistry
State University of New York at Potsdam Potsdam, New York
13676
The electrodeposition of copper on composi te conduct ive
polymer polypyrrole/polystyrenesulfonate PPy(PSS) has been studied.
The morphology of copper deposits was investigated in the presence
of thiourea, benzotriazole, boric acid, 1 ,&naphthalene
disulfonic acid, chloral hydrate, EDTA, and p-aminophenol. In the
presence of thiourea in the solution, the rate of copper deposition
on PPy(PSS) substrate was slightly inhibited but the rate of copper
stripping was faster than in its absence. The addition of
benzotriazole to the solution in mM concentration range results in
large separation between the deposition and stripping peaks. The
formation of Cu(l)-benzotriazole film in the intermediate potential
range was . confirmed with the Electrochemical Quartz Crystal
Microbalance and Voltammetric techniques.
The Electrochemical Quartz Crystal Microbalance (EQCM) technique
in conjunction with Scanning Electron Microscopy (SEM) was used.
The EQCM technique allowed us to simultanously monitor
voltamperometric and resonance frequency vs. potential or time
characteristics. The amount of electrodeposited copper was
controlled by monitoring the EQCM resonant frequency.
INTRODUCTION
Polypyrrole, a widely known conductive polymer, has a potential
to be a useful component of microelectronic devices. Polymers of
the polypyrrole type can be switched in a controlled way between
conducting and poorly conducting states. The possibilities of its
electronic applications would be substantially increased if metal
layers could be deposited onto the polypyrrole film. A few papers
appeared in the literature dealing with metallization of conductive
polymer films [ 1-91.
Among the variety of methods used in polymer metallization,
electrodeposition from aqueous solutions is very promising.
Electrodeposition of copper on a polypyrrole precoat formed by
chemical polymerization on an insulating substrate, with potential
applications for metallization of printed circuit boards has been
reported[2]. The electrodeposition of various metals on polypyrrole
carried out in typical industrial plating baths was examined by
cyclic voltammetry by Tan et al. [3]. The electrodeposition of
palladium, platinum, lead, and ruthenium on polypyrrole film was
reported by Pletcher e t al. [4]. Eiectrodeposition of nickel on
polypyrrole in the presence and absence of additives studied by the
EQCM technique has been investigated [ 5 ] . The effect of the
composition of polypyrrole substrate on the electrodeposition of
copper and nickel has been found[6].
The electrodeposition of copper is a process of great practical
importance,
1
709
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particularly in the electronics industry. However, the
deposition process is mechanistically very complex and the final
quality of copper electrodeposit depends on many interlinking
factors, including bath composition, convection, temperature,
current density and the presence of additives used as brightening
and levelling agents [IO-161. The presence of organic compounds in
an electrochemical system causes significant changes that affect
the nucleation process and growth of metal nuclei. For this reason,
many additives are used to optimize industrial electrochemical
plating processes. The most desired properties of deposits are
mirror-brightness, high-levelling, low internal stress of the
coatings, as well as, stability during use. Even trace levels of
additives present in the electroplating baths can import
tailor-made properties to the electrodeposits. In most cases, these
additives act as inhibitors in the electrodeposition process. The
purpose of this work is the investigation of copper
electrodeposition on conductive polymer using a new technique, the
Electrochemical Quartz Crystal Microbalance (EQCM) in combination
with scanning electron microscopy (SEM).
In this work, we report on electrodeposition of copper on
composite polypyrrole (PPy(PSS)) coated AU piezoelectrodes in the
presence and absence of additives. These data are compared with
electrodeposition of copper on unmodified gold electrodes. Using
the EQCM technique, we were able to follow changes in the electrode
mass by measuring the oscillation frequency of these
piezoelectrodes. in addition to the simultaneously recorded ,...
r..a-t L.UlIGIIL.
EXPERIMENTAL
An Electrochemical Quartz Crystal Microbalance (EQCM) with 10
MHz AT-cut quartz oscillators was used in this study. The EQCM is a
hybrid technique allowing for simultaneous monitoring of
voltamperometric and resonance frequency vs. potential or time
characterics. The EQCM technique is based
on the piezoelectric effect. The resonant frequency of the
quartz crystal lattice vibrations in a thin quartz crystal wafer is
measured as a function of the mass attached to the crystal
interfaces. For thin rigid films, the interfacial mass changes are
related to the changes in oscillation frequency of the EQCM through
the Sauerbrey equation:
A f = - 2Amnfo2
In this formula, the change in the resonant oscillation
frequency (Af) is equal to minus the change in the interfacial mass
(Am) per unit area (A) times a constant. Thus, the frequency
decreases as the mass increases. The constant is evaluated with
knowledge of the oscillation frequency of the fundamental mode of
the EQCM (fo), the overtone number (n), the density of quartz (dq =
2.648 g/cm3) and the shear modulus of quartz (pq = 2.947 x 1011 g
cm-1s-2). The EQCM is well suited to the measurements of mass
transport that can accompany redox processes occuring in thin rigid
films on electrodes [26-301. The excellent sensitivity and large
dynamic range of this device permit characterization of mass
transport (both ions and solvent) in films.
A model EQCN-700 Electrochemical Quartz Crystal Nanobalance
(ELCHEMA, Potsdam, NY) was used to monitor frequency variation
(mass changes) of piezoelectrodes. The active surface area of the
working Au electrode was 0.25 cm2. The oscillator crystals were
sealed to the side opening in a glass vessel of 30 mL capacity. The
working electrode was polarized using a Pt-wire coufiter electrcde
and its potentia! measured vs. a saturated calomel electrode (SCE).
A model PS-605 Precision I_ Potentiostat/Galvanostat (ELCHEMA) was
used in the measurements. The program waveform was generated and
measurements
acquisition system with 16-bit precision. The software trigger
utility of the VOLTSCAN was used to control precisely the amount of
deposited metal. This feature appeared to be
performed by VOLTSCAN real-time data - _^I
71 0 - 2 -
-
extremely useful for measurements oi nucleation density and
nuclei size which could have been done for the given amount (mass)
of deposit and irrespective of the deposition rate. The software
trigger allowed us to stop electrolysis after a given present mass
of the metal had been deposited. A Scanning Electron Microscope
MModel IS1 SX-40A was employed to obtain surface images of metal
depositions.
The electropolymerization of pyrrole was carried out on gold
piezoelectrode from aqueous electrolyte solutions containing 20- 70
mM pyrrole, and supporting electrolyte at constant potential E =
+600 mV vs. SCE and at E = +650 mV vs. SCE in the presence of
organic dopant, eg. poly(styrenesu1fonate) (PSS). Films with
thicknesses below 1 pm were typically grown. All chemicals were of
analytical grade purity and were used without further purification
except for pyrrole which was purified by distillation. Solutions
were prepared using Millipore Milli-Q deionized water. They were
deoxygenated by bubbling with purified nitrogen. All experiments
were performed at room temperature, 2 2 T .
RESULTS AND DISCUSSION
Electrodeposition of Copper on Composite Polypyrrole Without
Additives
The deposition of copper from 0. I M H2S04 solution without any
additives usually begins in the potential range from +lo0 to - iOG
mV vs. SCE. In this potential range, the composite PPy(PSS) film
electrode remains highly conductive and, thus, copper can be
readily deposited on such a film substrate.
In Figure 1, typical voltammetric and microelectrogravimetric
characteristics obtained for a PPy(PSS) modified Au-
EQCM electrode in 10 mM Cu(I1) -t 0.1 M H2S04 solution, are
presented. The increase in cathodic current observed during the
negative potential scan, at potentials less than E = -100 mV, is
accompanied by a simultaneous mass increase manifested on the
microelectrogravimetric curve. The cathodic peak potential is E, ,
= -140 mV and coincides with highest rate of mass increase on the
m-E curve. During the reverse potential scan, the copper stripping
begins at the potential, E = 0 mV, as
0.F
0.4
e t E cr
-0.4 B -0.8
3
-1.2
-1.6 J -800.0 -400.0 -0.0 400.0
Figure 1. Linear potential scan current vs. potential and mass
vs. potential characteristics for copper deposition on PPy(PSS)
modified Au- EQCM electrode obtained in 10 mM Cu(I1) + 0.1 M H,SO,
solution without additives, at scan rate v = 50 mV/s.
71 1
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demonstrated by the onset of the anodic current on the i-E curve
and the beginning of t h e m a s s d e c r e a s e o n t h e m - E
characteristic. The anodic peak potential E,,,, = +lo0 mV. The
total mass increase, dm = 3270 ng, due to the copper deposition,
corresponds to approximately 82.5 mono- layers of copper, assuming
that smooth deposit is being formed and the mean
M'/3N-'/3d2/-' = 201.7 ng/cm2, where M is the atomic mass of
copper, N is the Avogadro
- monolayer mass of copper is: mmon,, -
number, and d is the density of copper metal (d = 8.96 g/cm3).
As seen in Figure 1, the mass change in one potential cycle is not
well balanced, i.e. the final mass does not return to the initial
level. The current stripping peak also shows a long tail indicating
incompleteness of the stripping process. This is all caused by some
degree of the system's irreversibility.
In Figure 2, the results of cyclic chronoamperometric
experiments performed
0
-2.0
4 E c-; -4.0 i3 p: p: ' -6.0
-8.C
-1o.c
-800 -8OOmV - 8 0 0 m V
E
- 4000.0
0.0
I 400.0 800.0 1200.0
TIME, s
Figure 2 (a). Current and mass transients for sequential copper
deposition and stripping obtained on a Au-EQCM electrode in 10 mM
Cu(I1) + 0.1 M H,SO, solution without additives for potential steps
from E = +400 mV to E = - 800 mV and pulse duration tdep = 30
s.
-2.0 4 E
p: 0: 2
-6.0
8 E
-8.0 -
' -0.0 -10.0 400.0 800.0 1200.0
0
TIME, s
__ Figure 2 (b). Current and mass transients for sequential
copper deposition and stripping obtained on a Au-EQCM electrode in
10 mM Cu(I1) + 0.1 M H,SO, solution without additives for potential
steps from E = +400 mV to E = - 500 mV and pulse duration tdep = 30
s.
-~ __
4
71 2
-
on PPy(PSS) modified Au-EQCM electrode in 10 mM Cu(I1) + 0.1 M
H,SO, solution, are presented. In experiments of Figure 2 (a), the
electrode potential was stepped between E = -800 mV (deposition)
and E = +400 mV (stripping). Thus, the potential for copper
stripping is the same as the anodic potential limit E,, in
experiments of Figure 1. The deposition pulse duration was tdep =
30 s, and the stripping period was tdi,, = 370 s. As seen in Figure
2 (a), this longer dissolution time is more than sufficient to
allow all deposited copper to be removed from the electrode
surface. As expected, the amount of copper deposited is strongly
dependent on the electrode potential. This is confirmed by a
gravimetric characteristic presented in Figure 2 (b), obtained for
potential steps from E = +400 mV to E = - 500 mV. The mass of
copper deposited at the latter potential, at tde,, = 30 s, is 4000
ng, versus 6700 ng deposited at E = -800 mV, Figure 2 ( a ) . The
conductivity of polypyrrole is decreased at potentials more
negative than E = -500 mV. It is interesting to note that it does
not inhibit the copper electrodeposition process.
Effect of Thiourea
Thiourea is probably the most commonly used additive for copper
plating. In spite of the long history of its utilization and
numerous research studies performed [14-171, the detailed mechanism
of the brightening action of this additive is still not well
understood.
In Figure 3, a typical voltammetric and microelectrogravimetric
characteristics obtained for a PPy(PSS) modified Au- EQCM electrode
in 10 mM Cu(I1) + 0.1 M
H,SO, + 5.3 mM thiourea solution, are presented. The increase in
cathodic current observed during the negative potential scan, at
potentials less than E = -100 mV, is accompanied by a mass increase
manifested on the microelectrogravimetric curve. During the reverse
potential scan, the copper stripping begins at the same potential,
E = - 100 mV, as demonstrated by the onset of the anodic current on
the i-E curve and the beginning of the mass decrease on the m-E
characteristic. The total mass increase, dm
/
\ 2
.---- *c
100.0
bo C
!4 E
000.0
.o
800.0 -400.0 -0.0
POTENTIAL m V vs. SCE
Figure 3. Linear potential scan current Vs. potential and mass
vs. potential characteristics for copper deposition on PPy(PSS)
modified Au- EQCM electrode obtained in 10 mM Cu(I1) + 0.1 M H,SO,
+ 5.3 mM thiourea solution, at scan rate v = 50 mV/s.
5
71 3
-
= 2600 ng, due to the copper deposition, corresponds to
approximately 65.6 mono- layers of copper, assuming that a smooth
deposit is being formed. As seen in Figure 3, the mass change in
one potential cycle is well balanced, Le. the final mass value
returns to the initial level. This is indicative of t h e h i g h d
e g r e e of t h e s y s t e m reversibility. The experiments
performed on the same PPy(PSS) film electrode, under the same
conditions, but in the absence of thiourea
4.c
2 . [
( 4 E +- -2.1 E E 5 -4 .1
-6..
-E.(
-10.1
(Figure l), show a faster copper
200.0 400.0 600.0 800.0
T!ME, E
Figure 4. Current and mass transients for sequential copper
deposition and stripping obtained on a Au-EQCM electrode in 10 mM
Cu(I1) + 0.1 M H,SO, + 5.3 mM thiourea solution for potential steps
from E = +400 mV to E = -800 mV and pulse duration tdep = 30 s
.
deposition process, larger amount of copper deposited (3300 ng),
and a faster initial rate of dissolution. However, in the absence
of thiourea, the copper stripping peak has a more sluggish falling
branch (a longer tail) and, as a result, a rather large amount of
copper (1300 ng) remains undissolved at the end of the potential
cycle.
In Figure 4, the results of cyclic chronoamperometric
experiments performed on PPy(PSS) modified Au-EQCM electrode in 10
mM Cu(I1) + 0.1 M H2S04 + 5.3 mM thiourea solution, are presented.
The electrode potential was stepped between E = -800 mV
(deposition) and E = M O O mV (stripping). The deposition pulse
duration was tdeP = 30 s, and the stripping period was tdiss = 300
s. The amount of copper deposited is 4700 ng, substantially less
than in the experiment carried out under the same conditions in the
absence of thiourea (Fig- ure 2).
Effect of Benzotriazole
Benzotriazole has been shown to be one of the most effective
brightening agents for copper plating from sulfuric acid solutions
[11,17-201. The minimum concentration of benzotriazole in the
plating bath is usually around 0.1 mM. Our experiments were
performed using 10 mM Cu( I1 ) + 0.1 M H 2 S 0 4 + 1 . 3 m M
benzntriazznle. In Figure 5, voltammetric and
microelectrogravimetric characteristics obtained for a PPy(PSS)
modified Au- __ EQCM electrode, are presented. These
characteristics show a very complex behavior of this system. A
general conclusion which can be drawn from Figure 5 is that the
deposition and stripping processes are strongly irreversible in
the
6
71 4
-
presence of benzotriazole, in contrast to those in the presence
of thiourea. In order to analyze the system behavior in more
detail, we have to distinguish multiple potential regions in both
the cathodic going potential scan and the anodic potential
scan.
In the cathodic potential scan, four potential regions have to
be considered:
(A) from E = +400 mV to E = -110 mV; (B) from E = -1 10 mV to E
= -250 mV; (C) from E = -250 mV to E = -500 mV; (D) from E = -500
mV to E = -800 mV.
800.0 -400.0 -0.0
POTENTIAL, m-V m.
6000.0
4000.0
2
!! 2
2000.0
1.0
Figure 5. Linear potential scan current vs. potential and mass
vs. potential characteristics for copper deposition on PPy(PSS)
modified Au- EQCM electrode obtained in 10 mM Cu(I1) + 0.1 M H,SO,
+ 1.3 mM benzotriazole solution, at scan rate v = 50 mV/s.
The potential region A can be associated with the initial stage
of the copper deposition. It is represented on the i-E
characteristic by a rather sluggish prewave beginning at E = +150
mV. However, on the m-E characteristic, it is represented by a very
well defined wave with the major mass increase taking place from E
= +80 mV to E = -40 mV. The mass increase is cu. 800 ng. Further
mass increase ceases beyond E = -40 mV. This behavior could be
explained by assuming that benzotriazole is not adsorbed on the
PPy(PSS) film and during the initial copper deposition process it
gradually blocks the surface sites on the copper nuclei eventually
poisoning the surface completely and hindering further mass
increase. The potential region B can be ascribed to the onset of
copper deposition. It is manifested by a current peak with sharp
rising edge and a well defined mass wave, slightly higher than the
mass wave in region A. The onset of copper deposition in region B i
s undoubtedly associated with the breakdown of the tight blocking
film of benzotriazole and the following increase in the nucleation
density favored by the increasing cathodic overvoltage. The
potential region C is ascribed to a steady deposition process. It
is characterized on the m-E curve by a steady mass increase. The
i-E curve shows more complex behavior: a secondary current feature
burried on the falling branch of the main cathodic peak. In the
potential region D, we still have a steady deposition as evidenced
by a steady mass increase nn the 7n-E characteristic. The i -E
curve is again more complex showing a prewave at E = -620 mV and a
current rise near the cathodic potential limit, E,,,. Since this
prewave has no corresponding feature on the m-E curve, it can be
rationally ascribed to a Brdicka prewave. Similarly, the current
rise near E,,, has no resemblance on the m-E characteristic
7
71 5
-
and can be associated with the beginning of the hydrogen
evolution process.
In the anodic potential scan, four potential regions have to be
considered:
(E) from E = -800 mV to E = -200 mV; (F) from E = -200 mV to E =
+lo0 mV; (G) from E = +lo0 mV to E = +170 mV; (H) from E = +170 mV
to E = +400 mV.
The potential region E can be associated with the continuous
growth of the copper film. The m-E characteristic in this region
shows a steady mass increase, and the i-E characteristic shows a
steady cathodic current flow. The potential region F is perhaps the
most confusing. While the electrode is still gaining mass in a
steady fashion as indicated by the electrogravi- metric
characteristic, the current flowing is definitely anodic and
gradually increasing. To rationalize this anomalous behavior, we
have to recognize that the anodic current flow does not necessarily
mean that copper is being dissolved, but rather, in general, a
certain oxidation process is taking place. It is highly probable
that this anodic current is due to copper oxidation with formation
of sparringly soluble Cu(1) compound. Indeed, the formation of
Cu(1)-benzotriazole surface compound has recently been postulated [
171. The mass increase concomitant with the growth of such a
surface film must then take place due to the uptake of
benzotriazole as required by the compound stoichiometry. Thus, the
apparently anomalous behavior, actually confirms the formation of
Cu(1)- benzotriazole film formation. In the poten- tial region G,
the sharp anodic copper stripping peak accompanied by a step mass
decrease can be ascribed to the breakdown of the
Cu(1)-benzotriazole protective film. Since the mass decrease is
rather miniscule, it has to be concluded that either: (i) this
breakdown is not complete and that
rather limited amount of copper is released through crevices and
pinholes in the film still present on the surface, or: (ii) the
surface film Cu(1)-benzotriazole is oxidized and released from the
surface, i.e. both copper (as Cu2+) and benzotriazole, leaving the
underlying copper film with a clean surface, or: (iii) the surface
compound Cu(1)-benzo- triazole is oxidized but only copper is
released from the surface as Cu2+, whereas the freed benzotriazole
enters into another surface associate Cu"-benzotriazole hindering
any avalanche dissolution of the underlying copper film but not
blocking it entirely.
The microelectrogravimetric charac- teristic presented in Figure
5, confirms the mechanism (iii). Indeed, if the electrode surface
were freed from the benzotriazole, a spontaneous dissolution of
copper at potentials higher than E = 120 mV would result in large
current peak and mass decrease to the initial level (i.e., m = 0).
In the potential region H, copper dissolves slowly through the
adsorbed benzotriazole film.
Effect of Other Additives
The effect of other additives on the rate of copper deposition
on PPy(PSS) modified Au-EQCM electrode has also been studied. In
Table I , presented are results obtained in cyclic
chronoamperometric experiments with potential stepped between E =
+400 mV and E = -800 mV. The pulse duration for copper deposition
was tdeP = 30 s.
8
71 6
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TABLE 1. Mass of Copper Deposited from 10 mM Cu(I1) + 0.1 M
H,SO, solution Containing Different Additives, at a Constant
Potential E = -800 mV and tdep = 30 s
Additive Conc. Mass, ug
none 6.7 NDSA' 0.69 mM 8.7 EDTA 2.4 mM 6.0 C l 5.0 mM 5.0 %BO,
2.0 mM 6.0
' NDSA - 1,5-Naphthalene Disulfonic Acid.
The most inhibitive effect from this group of additives is
exerted by chloride ions, and the NDSA actually increases the rate
of copper deposition on PPy(PSS) film. Figure 6a: SEM micrograph of
Cu film
electrodeposited on PPy(PSS) gold modified EQCM electrode E =
-600 mV vs. SCE for 180 seconds from 10 mM CuSO4 +O.lM H2S04 + 0.63
mM thiourea solution. Effect Of Additives On Copper
Morphology
The SEM micrographs presented in Figure 6 (a)-(g) illustrate the
effect of various additives on the morphology of copper deposited
on PPy(PSS) modified Au- EQCM electrode from 10 mM Cu(I1) + 0.1 M
H,SO, solution containg: (a) thiourea, (b) benzotriazole, (c) boric
acid, (d) 1,5- naphthalene disulfonic acid, (e) chloral hydrate,
(f) EDTA, and (8) p-aminophenol. Thz copper deposit obtained in
soliiiion containing thiourea shows a microgranular structure with
the mean size of nuclei cu. 1 um. The effect of benzotriazole is
shown to reduce the intergranular distance. The deposit is very
smooth with virtually no tendency to form pores. In the presence of
boric acid in high concentration, also a
smooth deposit is being formed but some cracks and a tendency to
form dendritic clusters is visible. The deposit obtained in
1,5-naphthalene disulfonic acid is micro- crystalline, somewhat
similar to that obtained with added thiourea, but is more dense and
shows less empty channels. It is also more crystalline. The
addition of chloral hydrate to the copper plating solution also
produces a microcrystalline deposit with somewhat uneven
distribution of crystallites. In the presence of EDTA, copper
deposit with very small grains is formed but is covered with copper
flakes of varying size and shape. In solutions containing
p-aminophenol, two copper layers are clearly seen: the underlayer
with large fused spherical grains, and the
9
71 7
-
Figure 6b: SEM micrograph of Cu film electrodeposited on
PPy(PSS) gold modified E M M electrode at constant potential E
=
Figure 6c: SEM micrograph of Cu film electrodeposited on
PPy(PSS) gold modified EQCM electrode at constant potential E =
-\-- -
-600 mV vs. SCE for 180 seconds from lOmM CUSO,I to +0.1 M H7S04
+ 0.03 s/L
-600 mV vs. SCE for 600 seconds from lOmM CuSO4 + +0.1 M H2SO4 +
2mM -
benzotriazole iolution.
electrodeposited on PPy(P%Sj gold modified
boric acid solution.
Figure 6e: SEM micrograph of Cu film electrodeposited on
PPy(PSS) gold modified
EQCM dectrode at constant iotential E = -650 m M vs. SCE for 600
seconds from 1OmM CuSO4 + 0.1M H2SO4 + 0.2 g/L 1,5- naphthalene
disulfonic acid solution.
EQCM dectrode at constant potential E = -650 mV vs. SCE for 600
seconds from lOmM CuS04 + 0.1M H2SO4 + 0.4gL chloral hydrate
solution.
10
71 8
-
_-
Figure 6f SEM micrograph of Cu film Figure 6g: SEM micrograph of
Cu film electrodeposited on PPy(PSS) gold modified electrodeposited
on PPy(PSS) gold modified EQCM electrode at constant potential E =
EQCM electrode at constant potential E = -650 mV vs. SCE for 600
seconds from -650 mV vs. SCE for 600 seconds from lOmM CuSO4 + 0.1M
H2SO4 + 2.4 mM 10mM CuSO4 to +O.lM HzSO4 + 0.4 g/L p- EDTA.
aminophenol.
overlayer consisting of microcrystalline dendrites.
CONCLUSIONS
The experiments performed show that copper can be readily
deposited on the composite PPy(PSS) polymer surface and its
morphology can be controlled with a a variety of organic additives.
The main difference between the copper deposition on gold (and
other metal substrates) and on the PPy(PSS) surface lies in
different interaction of the latter surface with additives and with
copper. Thus the initial stage of the copper
nucleation process is mostly affected by the presence of the
PPy(PSS) film. The results obtained indicate that it is possible to
deposit on the surface of this polymer dense and smooth copper
films without any cracks or voids.
The Electrochemical Quartz Crystal Microbalance has proven tn be
an inva!~ah!e tool in studies of the electrodeposition process. In
conjunction with Voltammetry and Cyclic Chronoamperometry, the EQCM
technique allowed us to solve very complex behavior of systems with
various additives, including the interaction between additives, the
PPy(PSS) substrate and the copper deposit .
11
71 9
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ACKNOWLEDGEMENTS
This work was partially supported by the Research Corporation
Grant and the NATO Grant No. CRG 930020.
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