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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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The failure mode and Cu barrier properties of a 5 nm thick boron and carbon added Ru ͑Ru-B-C͒ film deposited on Si substrate have been investigated. Results from X-ray diffraction ͑XRD͒ and Fourier-transformed electron diffraction patterns indicate that the Ru-B-C film is amorphous up to 700°C. Unlike pure Ru film, the Ru in the Ru-B-C film recrystallized at 750°C instead of reacting with Si at the interface to form Ru 2 Si 3 . The sheet resistance and XRD results show that the 5 nm Ru-B-C barrier is thermally stable up to 750°C, whereas the 5 and 10 nm Ru are only stable below 550 and 600°C, respectively.Copper and porous ultralow-k ͑p-ULK͒ interconnects have been implemented in advanced integrated circuits ͑ICs͒ to reduce resistive-capacitive ͑RC͒ delay. 1,2 However, Cu can easily diffuse in porous materials. This deep-level trap can also propagate in silicon, which deteriorates device performance. 3-7 A highly reliable Cu barrier is required.The traditional Ta/TaN bilayer barrier has been widely adopted for IC production. Unfortunately, ever-decreasing feature sizes also create a demand for scaling of the copper barrier thickness. However, when barrier thickness is reduced to 1.7 nm for the 22 nm node technology, 8 the resistance of Ta/TaN films cannot meet the requirements of the International Technology Roadmap for Semiconductors. Furthermore, a reduced barrier cannot provide continuous film coverage on the rough sidewalls of p-ULK film in dual damascene structures. A barrier that is capable of Cu plating without a Cu seed layer allows a slightly thicker film ͑which is equal to the combined thickness of barrier and Cu seed layers͒ and is a promising approach to solve the above issues. Directly platable metals 9 include Ru, Pd, Pt, Rh, and Ir. Of these metals, Ru has a low resistance and is immiscible with Cu, 10 thus attracting much interest for use as a directly platable Cu barrier.However, pure Ru film exhibits poor performance as a Cu diffusion barrier due to its columnar microstructure, 11-14 which provides rapid diffusion paths for Cu atoms. A 20 nm Ru barrier can prevent Cu diffusion up to 450°C for 10 min, 11 whereas a 5 nm Ru film is only stable at 300°C for 10 min. 12,15 Recent studies of phosphorus-added Ru film demonstrated that 12 nm Ru͑P͒ can effectively block Cu diffusion above 700°C for 5 min, 16 and a separate study showed a similar effect at 300°C for 67 h. 17 This superior performance is attributed to the amorphous microstructure that results when phosphorus is added. A 15 nm Ru-Ta layer effectively blocked Cu diffusion up to 600°C for 30 min. 18 A plasma-enhanced atomic layer deposited 10 nm amorphous Ru 0.58 -͑TiN͒ 0.42 film was stable at 700°C over a 30 min anneal. 19 Ternary alloys tend to have higher recrystallization temperatures because grain nucleation is delayed by an added third element. 20,21 To our knowledge, an ultrathin ͑ϳ5 nm͒ robust Ru-based seedless barrier deposited on Si substrate, which is more sensitive to sheet resistance value, has not yet been reported.In this articl...