EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Alternative barrier layers have been considered to replace Ta/TaN, such as Ru and Co-based binary systems, e.g. Ru W, Ru-Mn, and Co W, in Cu interconnect metallization. The Co-W system is an interesting candidate to novel barrier materials due to its electrical and thermal properties. Co-W can function as both, the diffusion barrier and the seed layer whereon Cu can be directly electroplated, but this is a frankly unaddressed topic. This work consists of an introductory approach to the Cu electrocrystallization on top of Co W thin films using acidic electroplating baths, focusing on the initial stages of electrodeposit formation. Cu was directly electrodeposited (ED) on Co-W(PVD)/SiO2/Si substrates using a conventional acidic electrolyte, by direct and pulsed current. Co-W and Cu films were characterized by SEM/EDS, AFM, XPS and optical microscopy. The results show that the acidic nature of the solutions dissolves the Co-W substrate, but particularly Co is dissolved quicker than W. Through this mechanism, the nucleation of Cu decreases over time, rendering incomplete/discontinuous substrate coverage. A balance between Cu nucleation and substrate dissolution dictates the final soundness and compactness of the Cu films, which can be improved by decreasing substrate dissolution rate, using less aggressive/acidic solutions of pH 3.5.