Evaluation of Adhesion Properties of Electrodeposited Copper Thin Films: Theoretical and Experimental Approach

The adhesion of copper thin films galvanostatically electrodeposited on Cu cathodes from electrolytes without or with the addition of various additives, such as chloride ions, polyethylene glycol 6000 (PEG 6000), and 3-mercapto-1-propanesulfonic acid, has been investigated. Morphological and structural analyses of synthesized films were performed using the SEM, AFM, and XRD methods, while the adhesion of the films was examined by applying the theoretical Chen-Gao (C-G) composite hardness model using results from Vickers microindentation, a bidirectional bending test, and a scratch-tape adhesion test. The morphologies of the films were either very smooth, with mirror-like brightness, obtained from the electrolyte containing all three additives, or microcrystalline, with different grain sizes, obtained from other electrolytes. The best adhesion was observed in the fine-grained film with numerous boundaries among grains, obtained with the addition of chloride ions and PEG 6000, while the mirror-bright film obtained with a combination of all three additives showed the worst adhesion. The boundaries among grains represented barriers that decreased the depth of penetration during microindentation and, consequently, increased the hardness and enhanced the adhesion of the film. The size of the grains-and hence, the number of grain boundaries-was regulated by the composition of the electrolytes achieved by the addition of additives. Good agreement was observed among the various methods used for the estimation of the adhesion properties of Cu films.