Electrochimica Acta 54 (2009) 5889–5893
Electrochimica Acta
Electroless plating of aluminum using diisobutyl aluminum hydride as liquid
reducing agent in room-temperature ionic liquid
Isao Shitanda∗, Atsushi Sato, Masayuki Itagaki, Kunihiro Watanabe, Nobuyuki Koura
Department of Pure and Applied Chemistry, Faculty of Science and Technology, Tokyo University of Science, 2641, Yamazaki, Noda-shi, Chiba 278-8510, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
We investigated an electroless aluminum plating based on using AlCl3–1-ethyl-3-methylimidazolium
chloride (AlCl3–EMIC) ionic liquid with diisobutyl aluminum hydride (DIBAH) as a liquid reducing agent.
The plating film was analyzed by measurements of X-ray diffraction, scanning electron microscopy with
energy-dispersive X-ray analysis (SEM-EDX) and glow discharge optical emission spectroscopy (GD-
OES). Consequently, a thick aluminum plating film with high uniformity was prepared from AlCl3–EMIC
with DIBAH. No impurity phases were detected. Moreover, we discussed the reaction mechanism of the
electroless aluminum plating.
Received 21 January 2009
Received in revised form 26 April 2009
Accepted 13 May 2009
Available online 21 May 2009
Keywords:
Room-temperature ionic liquid
Aluminum
© 2009 Elsevier Ltd. All rights reserved.
Electroless plating
1. Introduction
soluble in the plating bath and accompanied with excessive fever
Aluminum is used for many electronic-equipment, including
hard disks, compact disks, high-density memory devices, semi-
conductor devices, electronic circuitry [1,2] since aluminum has a
superior characteristic in corrosion resistance, thermal and electric
conductivity. There are many uses of aluminum thin films but it is
necessary to use large reactors utilizing methods such as sputter-
ing and glow plasma in order to deposit aluminum on an insulating
substrate such as silicon or glass.
Electroless plating is potentially useful method to produce alu-
minum thin films and aluminum wiring at the lowest cost. If the
technique for electroless plating of aluminum is established, it will
be able to obtain the thin and thick film coating on the substrates
of insulating material and of quite complicated structures without
at the deposition reaction.
We also found a liquid reducing agent: diisobutyl aluminum
hydride (DIBAH, chemical structure: Fig. 1) [7]. They mentioned
that a smoother plating surface was obtained in the case of DIBAH
compared with the case of LiH. However, there were no reports of
the details such as plating condition, film composition and reaction
mechanism.
In the present study, we investigated the aluminum electroless
plating based on using DIBAH which is highly soluble in AlCl3–EMIC
ionic liquid. We verified that a dense aluminum film with smooth
surface could be plated uniformly by using DIBAH. The plating bath
containing DIBAH was easier to control than that containing LiH. In
addition, the reaction mechanism of electroless aluminum plating
with DIBAH was discussed.
It is impossible to obtain electrodeposition of aluminum in an
aqueous solution because aluminum is a less-noble metal. Alu-
minum can be deposited from a room-temperature ionic liquid
(RTIL) [3–6], but a practical technology for depositing aluminum
from RTIL has not been established. Recently, we developed a
technique for the electroless plating of aluminum based on using
AlCl3–1-ethyl-3-methylimidazolium chloride (EMIC) ionic liquid
and lithium hydride (LiH) as the electrolyte and the solid reducing
agent, respectively [7]. An aluminum film was formed on a glass
surface without any impurity phase. On the other hand, the plating
2. Experimental
A glass plate and a copper sheet were used as the substrates.
We pretreated the substrates by the following procedures. First, the
substrate was polished with Emery paper (#320) and then washed
in turn with methanol and acetone. Second, the substrate was sen-
sitized in acidic SnCl2 solution (0.127 mol dm−3, pH 0.74) for 5 min.
Third, the surface of the substrate was activated in acidic PdCl2
solution (1.69 mmol dm−3, pH 0.77) for 5 min. The acidity of each
solution was controlled by hydrochloric acid.
The AlCl3–1-ethyl-3-methylimidazolium chloride ionic liquid,
used as the electrolyte, was synthesized with the following pro-
cedures. First, AlCl3 and 1-ethyl-3-methylimidazolium chloride
∗
Corresponding author.
0013-4686/$ – see front matter © 2009 Elsevier Ltd. All rights reserved.