Influence of additives on Cu thin films electrodeposited directly on Ti diffusion barrier in Cl−-free electrolytes for Cu interconnect

Abstract

For Cu interconnect in Si-based microelectronic devices, seedless electrodeposition of Cu thin films directly on Ti diffusion barrier was investigated in Cl−-free, citrate (Cit)-based acidic electrolytes with polyethylene glycol (PEG) or Janus Green B (JGB) additive. Both PEG and JGB suppressed Cu electrodeposition on the Ti surface effectively, and even their inhibition against Cu-Cit complex reduction was synergetic. Accordingly they decreased the surface roughness of Cu thin film on the Ti surface considerably. Thus, seedless growth of Cu thin films on Ti was achieved from the synergistic leveling effect of both PEG and JGB in the absence of Cl− because PEG adsorption onto the Ti surface did not accompany PEG complexation with Cl− and Cu+, and CuCl contamination did not occur. 3D nucleation of Cu on the Ti surface became more progressive in more additive-concentrated electrolytes. Good interfacial adhesion between Cu thin film and Ti diffusion barrier was maintained, whereas the sheet resistance of Cu thin films was fairly increased, in spite of adding PEG and JGB.