Solution studies of systems with polynuclear complex formation. 1. The copper(II) citrate system

On the origin of the spontaneous potential oscillations observed during galvanostatic deposition of layers of Cu and Cu2O in alkaline citrate solutions

“…With formation constants taken from Daniele et al [13], Rode et al [12] concluded that the dimer [Cu 2 H À2 Cit 2 ] 4À is the predominant species at pH values greater than 7, in the excess of citrate. This is also in agreement with the results of other findings [14][15][16][17][18]. In analogy with the lactate and tartrate cases, the b-hydroxyl proton is restored when the complex dissociates upon the deposition of copper from a Cu(II)-citrate solution.…”

“…Such information is available in the literature [12][13][14][15][16][17][18][19] and based on these studies the predominating complex in the present solutions can be identified. Regarding the reasons for the oscillations, it is reasonable to assume that these are caused by changes in the pH in the vicinity of the electrode as was described by Leopold et al [4] for the corresponding Cu(II)-lactate system.…”

“…[4], it is likewise important to study other oscillating systems than the lactate and tartrate systems studied so far. From this point of view, the Cu(II)-citrate system appears to be an interesting candidate, particularly as reliable speciation data regarding the Cu(II)-citrate system are available in the literature [12][13][14][15][16][17][18][19]. We are, however, not aware of any previous report of the attainment of this type of oscillations in the Cu(II)-citrate system.…”

Electrochemical Behavior of Citric Acid and Its Influence on Cu Electrodeposition for Damascene Metallization

“…This allowed for the calculation of proton concentrations, which were found to be 0.0251, 0.0437, 0.0724, and 0.100 M. Note that the calculated concentrations were below the amounts of corresponding citric acid; since citric acid is triprotic, three dissociated forms (H 2 Cit − , HCit, 2− and Cit 3− ) are possible, with the predominant structure being determined by electrolyte pH. Since the dissociation constants of citric acid are 2.79 (pK 1 ), 4.30 (pK 2 ), and 5.65 (pK 3 ), 40 it is reasonable to conclude that the main forms of the citrate species in the electrolyte were H 3 Cit and H 2 Cit − . While the former does not generally form complexes with Cu, the latter is able to do so.…”

“…It has been reported that the complex formed between Cu ions and citrate is dependent on the pH of the electrolyte and the concentration ratio between Cu ions and citrate. [40][41][42][43][44] For pH < 2, no complex was observed as the citric acid largely favored its neutral, non-dissociated form. However, once pH>2, citric acid dissociated to H 2 45 Complex formation can be ob- served through UV-vis spectroscopy, with absorption at 800 nm being associated with hydrated, non-complexed Cu ions, and a blueshift and intensity increase being associated with complex formation.…”