Effect of Halides on Cu Electrodeposit Film: Potential-Dependent Impurity Incorporation

Abstract

In this study, the effect of halides (X = Cl−, Br−, and I−) on the electrodeposited Cu film properties such as film resistivity, crystal structure, and impurity were evaluated. The resistivity of the Cu film electrodeposited with iodide in the plating electrolyte increased significantly, whereas the resistivity of the Cu film electrodeposited with chloride and bromide remained unchanged. Scanning electron microscopy, X-ray diffractometry, atomic force microscopy, and X-ray photoelectron spectroscopy analyses of the Cu electrodeposit films indicated that the increase in the resistivity with the addition of iodide originated from its incorporation into the film. CuX precipitate as a plausible impurity species, would be simultaneously removed via the reductive dissolution during Cu electroplating. Therefore, high impurity level for iodide would be associated with more negative reduction potential for CuI compared to those of CuCl and CuBr. It was supported by the potential-dependency of the impurity level and the resistivity of Cu film electrodeposited with iodide where the more negative deposition potential resulted in the less resistivity. The impurity level of CuI in Cu film was estimated via Mathiessen's rule in the range of a few μM in the electrolyte.