The deposition of copper (Cu) on aluminum (Al) is important for submicron interconnects and plating treatments of Al-based substrate. While aqueous deposition of Cu on Al is challenging on several technological and environmental problems. In this paper, we described electroless deposition of Cu onto Al surface through galvanic replacement from a simple and stable choline chloride (ChCl) based ionic liquid comprising a 1:2 stoichiometric mixture of ChCl and ethylene glycol (EG). Thermodynamic feasibility of Cu deposition by galvanic replacement on Al in ChCl-EG ionic liquid was studied by cyclic voltammetry. The effect of thiourea (TU) on the kinetics of galvanic replacement and the characterization of Cu layers were investigated by open circuit potential (OCP), electrochemical noise (ECN), scanning electron microscopy (SEM) and X-ray diffraction (XRD). Results showed that sustained deposition of Cu on Al surface was achieved in both the ChCl-EG ionic liquid solutions without and with addition of TU. The presence of TU in the ionic liquid restrained the galvanic replacement process, resulting in obtaining a compact and uniform Cu layer on Al surface.Copper (Cu) is proposed as an interconnect metal for submicron integrated circuit technology due to its lower electrical resistivity compared to Al (∼1.7 vs. 3.0 μ · cm) and higher resistance to stressinduced voiding and electromigration. 1-4 The deposition of Cu metal onto Al has been developed as an important industrial process. In addition, the deposition of Cu is commonly used as a pretreatment method for coatings of Al substrates in order to obtain well-adhering coatings by substituting the naturally formed oxide film of Al. 5-7 The most common methods of producing Cu layer include electroplating 7,8,9 and electroless deposition. 10-12 Among them, electroless deposition is of special interest due to the advantages such as uniform deposition, convenient operation and a relatively low cost.Typical electroless deposition occurs through reduction process of metal ions in the presence of a reducing agent, which has been applied to many areas due to its low cost, low temperature process and simplified procedures. However, the process relies strongly on the composition of plating bath, which contains complex agent, reducing agent, some catalysts in addition to metal salts. 11 In the case of electroless Cu deposition, the conventional processes are usually related to technological and environmental problems. For example, the stability of the plating bath is not good enough. Some copper (II) ligands, reducing agents and acids, such as formaldehyde and hydrofluoric acid are not environmentally friendly. Moreover, the use of strong acids has an additional detrimental effect because of the etching of the substrates. [13][14][15] As a type of electroless deposition, galvanic replacement process has been explored for the growth of Cu layers on Al. 6,16 During the course of a galvanic replacement, the process occurs spontaneously and the reducing electrons are derived from the b...

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