D52 ECS Electrochemistry Letters, 2 (11) D52-D54 (2013)
2162-8726/2013/2(11)/D52/3/$31.00 © The Electrochemical Society
Tailored Design of Suppressor Additives for Copper Plating
by Combining Functionalities
Nguyen T. M. Hai,
z
F´ elice Janser, Nicola Luedi, and Peter Broekmann
*
Department of Chemistry and Biochemistry, University of Bern, Bern 3012, Switzerland
An extraordinarily strong suppressor additive (IPEG) for copper plating has been synthesized by the copolymerization of imidazole
and poly(ethylene glycol) diglycidyl ether (PEG-DGE). This new IPEG polymer contains the typical functional groups of both PAG
(poly(alkylene glycol)) and IMEP (polymerizate of imidazole and epichlorohydrin) polymers. The new IPEG polymer combines the
properties of PAG (typical suppressor for Damascene applications) and IMEP (state-of-the-art leveler for Damascene applications).
The combination of two suppressing modes of action in a single polymer results in significant enhancement of the suppressing
capacity of this new IPEG polymer over that of conventional suppressors and levelers.
© 2013 The Electrochemical Society. [DOI: 10.1149/2.005311eel] All rights reserved.
Manuscript submitted July 22, 2013; revised manuscript received August 7, 2013. Published August 16, 2013.
Additives are important for industrial copper plating processes
such as the Damascene process
1,2
or the fill of Through-Silicon-Vias
(TSVs).
3–5
A typical copper bath for Damascene applications uses
chloride-activated polyalkylene glycols (PAGs)
2,6–11
as suppressor ad-
ditives (polarizers) and SPS (bis-(sodium-sulfopropyl)-disulfide) and
its dissociation product mercaptopropane sulfonic acid (MPS) as a
specific antagonist (depolarizer).
2,9
However, “bumps” appear as a
side effect on the top of the filled features or on a dense array of
small features. To prevent “bump” formation over the features, an
additional leveling agent, usually a nitrogen-containing organic com-
pound/polymer, is used in addition.
12,13
According to the classification
of suppressor additives based on synergistic and antagonistic ensem-
ble effects, PAG based suppressor additives are considered as type
I suppressors due to a purely antagonistic suppressor /SPS(MPS)
interplay.
14,15
Classic leveling reagents such as polyethyleneimines
are considered as type II suppressors due to their purely synergistic
suppressor/SPS(MPS) interplay.
14,15
The polymerizate of imidazole
and epichlorohydrin (IMEP) is one such state-of-the-art leveler ad-
ditive which has a hybrid characteristic between type I and type II
suppressors.
15,16
This additive achieves active selectivity rapidly in
the region where the “bumps” should be prevented. Copper films
deposited in the presence of such an IMEP leveler show low contam-
ination levels compared with classic levelers.
16
The present work aims to combine the functional groups of the PEG
suppressor and state-of-the-art IMEP leveler in a novel suppressor
additive. This attempt has been achieved using the reaction of glycidyl
with amine functional groups.
17–19
Our electrochemical experiments will demonstrate that the new
polymer has hybrid characteristics and a strong suppressing capacity
for copper plating.
Experimental
SPS (bis-(sodium-sulfopropyl)-disulfide, Raschig, Ludwigshafen,
Germany) was purified by recrystallization before use. IMEP
(polymerizate of imidazole and epichlorohydrin) with the average
M
n
7 kDa and PAG (polyalkylene glycol) with M
w
8.4 kDa were pro-
vided by BASF SE Electronic Materials (Ludwigshafen, Germany).
Imidazole 99% and PEG-DGE (poly(ethylene glycol) diglycedyl
ether) with the average M
n
0.526 kDa from Aldrich were used without
further purification. Other solvents and reagents (H
2
SO
4
96%, Merck,
suprapur; HCl 30%, Merck, suprapur; CuSO
4
· 5H
2
O, Sigma-Aldrich
and DMSO, Sigma-Aldrich) are analytical grade.
The novel copolymer has been synthesized using the glycidyl-
amine reaction
17–19
between imidazole and poly(ethylene glycol)
diglycidyl ether (PEG-DGE) (Fig. 1). Imidazole (0.1 mol) and PEG-
DGE (0.1 mol) were added into 200 mL absolute ethanol in a round
bottom flask. The resulting solution was stirred at 200 rpm and heated
*
Electrochemical Society Active Member.
z
E-mail: thi.nguyen@dcb.unibe.ch
to 60
◦
C for 6 h. The solvent was removed by rotary evaporation and
dried overnight under vacuum at 10
−2
mbar.
1
H-NMR measurements
(Bruker Avance 300 MHz) of the reactants and product in DMSO
were performed. Imidazole:
1
H NMR (300 MHz, DMSO) δ 12.03 (s,
1 H), 7.63 (s, 1 H), 7.0 (s, 1 H) and PEG-DGE:
1
H NMR (300 MHz,
DMSO) δ 3.72 (dd, J = 14.4 Hz, 6 H), 3.53 (m, J = 12.3 Hz, 69 H),
3.28 (q, J = 26.7 Hz, 5 H), 3.11 (m, J = 16.2 Hz, 4 H), 2.73 (m,
J = 9.3 Hz, 4 H), 2.5 (m, J = 15.6 Hz, 7 H)). NMR analysis of
the IPEG product:
1
H NMR (300 MHz, DMSO) δ 7.5 (s, 1 H), 7.1
(s, 1 H), 6.8 (s, 1 H), 3.5 (m, J = 51 Hz, 68 H), 1.05 (m, J = 26.1 Hz,
7 H).
Electrochemical measurements were performed using an Autolab
potentiostat/galvanostat (PGSTAT 128) and a three-electrode cell con-
sisting of a Pt rotating disk electrode (RDE), Pt counter electrode, and
Ag|AgCl|KCl
3M
reference electrode. The preparation of a copper pre-
plated Pt electrode and additive-free copper bath (denoted as Virgin
Makeup Solution (VMS): 10 g/L H
2
SO
4
, 50 ppm chloride and 40 g/L
Cu
2+
) have been described elsewhere.
14,16
Results and Discussion
NMR analysis reveals the purity of the reactants and the reaction
product, apart from some solvent residuals (ethanol). The appearance
of the desired reaction product was confirmed due to the disappearance
of the characteristic peaks of the reactants, especially the imidazole
NMR resonance at 12 ppm. All expected resonances of the synthesized
IPEG polymer could be identified, particularly peaks from the three
hydrogen atoms bound to the imidazole moiety with shifts of 6.8, 7.1
and 7.5 ppm.
IPEG as a strong suppressor additive.— The suppressing ca-
pacities of the new polymer and reactants were investigated using
potential transient measurements with constant current density of
J =−10 mA/cm
2
.
14,20
In this context, the suppressing capacity is de-
fined as the difference between the overpotentials achieved in tran-
sient measurements in the presence and absence of additives at the
given galvanostatic copper plating conditions. Fig. 2 demonstrates that
imidazole nearly lacks suppressing capacity toward galvanic copper
deposition (curve 1). In contrast, the initial PEG-DGE polymer shows
a quite strong suppressing capacity, with an increase in the overpo-
tential of E =−172 mV (curve 2). Surprisingly, the IPEG polymer
demonstrates the strongest suppressing capacity reported, with an in-
EtOH
60 C
o
N NH +
N
+
N
*
OH
O
O
OH
*
O
O
O
O
m
m n
n n
Imidazole PEG-DGE IPEG
Figure 1. The synthetic route of IPEG from imidazole and poly(ethylene
glycol) diglycidyl ether (IPEG-DGE).
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