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Barrier properties of 10 nm thick Ru and amorphous Ru 37.2 W 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 ͑XRD͒ 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 37.2 W 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 WO 3 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 37.2 W 62.8 film is an alternative candidate for the Cu direct platable seedless barrier in the advanced copper metallization process.As continuous shrinkage of the integrated circuits ͑IC͒ feature size, resistive-capacitive ͑RC͒ delay is a dominant factor affecting switching speed for advanced IC. To reduce RC delay and enhance electron migration ͑EM͒ resistance, the integration of copper interconnects with porous ultralow-k dielectric has been implemented. 1 Traditional physical vapor deposited ͑PVD͒ Ta/TaN bilayer films were adopted as a copper diffusion barrier for the Cu metallization process. 2-4 However, the conventional copper process requires a Cu seed layer, which creates process complexity as well as poor Cu filling for more aggressive interconnects, such as 22 nm technology node and beyond. The wiring resistance also has difficulty meeting electrical design rules. Ruthenium ͑Ru͒, a direct platable noble metal, was extensively investigated as a Cu seedless diffusion barrier. 5-7 However, the thermal stability of a pure Ru film was poor against Cu diffusion due to its columnar grains, which provided rapid diffusion paths for copper atoms. 5,8,9 To improve Ru barrier performance and preserve its direct platable properties, Ru was doped with nitrogen 9,10 and phosphorus 11-14 to transform the Ru film into an amorphous-like microstructure. Ru-Ta-based alloy has desirable wettability with Cu and great gap-filling capability for Cu electrochemical plating. 15,16 Its capability to block Cu diffusion was improved because of its amorphous-like microstructure. 17,18 An interconnect using RuTa barrier was also reported to have a longer EM lifetime. 16,19 Both ruthenium and tungsten have negligible solubility in Cu, 20 and their resistivities are lower than that of the traditional Ta/TaN barrier. Studies of the Ru/W system 21 indicated a W alloy with 15 or 65 atom % Ru was crystalline at room temperature. In this paper, thermal stability of RuW films with various composition ratios ͑Ru within 15-65 atom %͒ is studied. The microstructure and phase transformation of amorphous Ru 37.2 W 62.8 film are reported. Significant barrier perform...

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