On the Role of Poly(ethylene Glycol) in Deposition of Galvanic Copper Coatings

Abstract

SummaryA literature review is provided of the influence and the behaviour of polyethers of the type of polyethylene glycol (PEG) and polypropylene glycol (PPG) on electro deposition of copper coatings in acidic electrolytes. Emphasis is given to the scientific understanding of various phenomena associated with the processes being discussed. The topics include the influence of PEG (PPG) (alone or in the presence of Cl−) on the kinetics of the electrocrystallization process as a function of: degree of cathode polarization; molecular weight and concentration of PEG (PPG) and of chloride ions. The probability of complex formation of Cu+ and Cu2+ with PEG (PPG) and Cl− is also discussed.Based on an analysis of published literature data it is shown that: (i) PEG (PPG) strongly inhibits the cathodic process; (ii) there exists a critical potential (on cathode polarization) which is responsible for the great difference in the degree of suppression of the deposition current in the presence of PEG (PPG); (iii) in the presence of Cl− in the electrolyte, the potential region within which PEG (PPG) is adsorbed most readily increases dramatically.The possibilities of complex formation between Cu+(Cu2*) ions and PEG (PPG) in the absence and in the presence of Cl− are also discussed. It is pointed out that the presence of PEG (PPG) in the acidic electrolytes for copper electrodeposition leads to the formation of complexes of the type(/Cu+(-CH2-)3.H2O) and {Cu2++(-CH2-)3.2H2O} as well as to a significant increase in concentration of the so called “ate”-complexes (CuCl2−, CuCl32-, CuCl+, CuCl42-). The formation of such complexes and their possible adsorption on the cathode surface are proposed as an explanation for the effect of suppressing copper deposition current.