Electrical evaluation of Ru-W(-N), Ru-Ta(-N) and Ru-Mn films as Cu diffusion barriers
Co-sputtered Ru-Ta(N), Ru-W(N) and Ru-Mn composites are investigated in terms of their barrier properties against Cu diffusion. A wide range of stoichiometries is analyzed with regard to crystallization, barrier properties, resistivity, Cu adhesion and direct Cu plating behaviour. All films were annealed at 350 °C and 600 °C in forming gas for 1h and subsequently stressed at elevated temperatures and electrical fields (BTS, 250 °C, 2 MV/cm, 30 min). The leakage current was monitored during BTS to observe increased leakage due to Cu diffusion. The Cu ions that eventually have passed the barrier and drifted into the dielectric of the MIS test structure were detected and quantified using the triangular voltage sweep method. The addition of 10% W or Ta into a Ru film already leads to a highly improved barrier performance against Cu diffusion, comparable to TaN, as long as the temperatures involved are kept below 350 °C. Outstanding barriers were identified after 600 °C anne aling and subsequent BTS, among them Ru50W50, Ru50Ta50 and Ru95Mn5. However, only Ru90Ta10 and Ru95Mn5 offer an excellent Cu adhesion and the possibility of direct Cu plating.