Surface Morphology Evolution of Cu Thin Films Electrodeposited Directly on Ti Diffusion Barrier in Citric Acid

Abstract

The formation of Cu thin film directly on Ti diffusion barrier by electrodeposition is important for next generation Cu interconnect in Si-based microelectronic devices. It depends on the surface morphology evolution of Cu deposit at the initial stage of nucleation and growth. In this study, we investigated the surface morphology evolution of Cu thin film on Ti in citric acid solution, introducing several simple ways to determine the stages of nucleation, Cu nuclei overlap, and Cu film formation with deposition time. During potentiostatic Cu deposition, studies on morphology change using the chronoamperometry, the change of surface roughness, and the change of sheet resistance and sheet resistivity are carried out along with microscopic observation. Resultant surface morphology of Cu deposit on Ti is greatly influenced by nucleation behavior, and its dependence on deposition potential is also studied in relation with the calculation of critical Cu nucleus size. According to the suggested ways, it is available to indirectly observe the transition of Cu nuclei to Cu thin film on Ti diffusion barrier during electrodeposition.