Electrodeposited copper using direct and pulse currents from electrolytes containing low concentration of additives

This work examines the effect of pulse deposition using a “lean” electrolyte, i.e., an acid-free bath with low cupric ion and additive concentrations using direct and pulse current. To this end, 25 μm copper films have been plated on stainless steel substrates from electrolytes containing only cupric ions, chloride and commercial additives. Films have been deposited from electrolytes containing different concentrations of additives ranging from 17% to 200% of the levels recommended by the supplier. The morphology of deposits was characterised using scanning electron microscopy and grain size has been determined using electron backscattered diffraction (EBSD). The crystalline structure has been examined using x-ray diffraction (XRD). It was found that although pulse currents or increasing amounts of chemical additive can reduce the grain size, the mechanisms for size reduction may be different. Whilst current pulsing helps the generation of new nuclei, using additives suppresses grain growth. Mechanical and electrical measurements of these films showed that pulsing currents provide deposits with better mechanical and electrical properties. This has been attributed to lower number of defects when pulse currents are used. Our results also show that by using pulse currents, electrolytes containing low levels of additives and metal ions can be used to obtain copper deposits attaining industry specifications. Combining pulse currents with lean electrolytes may be therefore beneficial to the environment.