The properties of the polyethylene glycol complex PEG(Na+)(Cu+) on the copper electrodeposited layer by Time-of-Flight Secondary-Ion Mass Spectrometry. The new insights

Abstract

The properties of polyethylene glycol PEG(Na+)(Cu+) complex on the copper electrodeposition layer was studied by Time-of-Flight Secondary-Ion Mass Spectrometry (TOF-SIMS). The most stable PEG(Na+) fragment, C11H22O6Na+, consists of the central sodium ion surrounded by six ethereal oxygens atoms completed with a pseudo-crown ring. The mechanism of fragmentation pathways leading to the characteristic fragments for complexes PEG(Na+) and smaller fragments PEG(Cu+) was extensively discussed. The adsorption of PEG onto copper is stabilized by counterion effect of sodium ion with the chloride adlayer and hydrophobic interaction. Hydrophobic groups can be oriented towards the chloride adlayer, whilst ethereal oxygen with central sodium ion towards the electrolyte. Consecutively, additional bonds between ethereal oxygen of PEG and copper ions Cu+ (in the CuCl form), identified as a fragments C4H8O2Cu+, stabilize and increase adsorption of PEG molecules. The substitution of HCl as a source of Cl− onto NaCl at adjusted Cl− concentration, diminishes the suppressing abilities of PEG. Under an optimal Na+/Cl− ratio adsorption of PEG also occurs under an open circuit potential. The mechanism of the interaction between complex PEG(Na+)(Cu+) and the chloride adlayer and its importance for a suppressing abilities was provided. Adsorption of PEG(Na+) is strongly dependent on the applied electrode potential. It was also demonstrated that nine charged sodium sites are separated by linking chains, consisting of approximately 12 monomer CH2CH2O units. Our results show that the contamination of copper sulfate by sodium ions plays an important role as a source of sodium ion in forming pseudocrown ethers by polyethylene glycol. Due to this reason, the optimization protocols for suppressing abilities of PEG should take into account molar ratio Na+/Cl− as well as their concentrations. The study proves that a combination of cyclic voltammetry (CV) with TOF-SIMS under the static regime, where substrate wire is withdrawn from a bath in a controlled manner under electrodeposition condition is an extremely powerful tool for the evaluation of changes in chemistry species on the copper surface under real electrodeposition condition.