Amorphous RuW film as a diffusion barrier for advanced Cu metallization

Barrier properties of 10 nm thick Ru and amorphous Ru_37.2W _62.8 films as seedless copper diffusion barriers have been investigated. Thermal stability of the barriers was evaluated after annealing at various temperatures. X-ray diffraction (XRD) analyses and sheet resistance measurements suggested that the Ru_37.2 W_62.8 barrier was thermally stable up to 700°C against Cu diffusion, which improved about 150°C over the Ru film. XRD studies and electron diffraction patterns of the Ru_37.2W_62.8 film showed that it maintained an amorphous-like microstructure after 30 min annealing at 550°C. This film started to recrystallize at about 600°C and developed to a film with Ru and WO₃ grains after a 700°C anneal. The leakage current of the 500°C postannealed Cu/RuW/porous SiOCH/Si stacked structure provided nearly 2 orders of magnitude superior than that of the Ru sample. The amorphous Ru _37.2W_62.8 film is an alternative candidate for the Cu direct platable seedless barrier in the advanced copper metallization process.