A sputter-prepared Ru ͑7 nm͒/WN x ͑8 nm͒ stacked layer was investigated as a diffusion barrier layer between Cu and Si for direct-plateable Cu interconnects, and its performance was compared with that of a Ru single layer with the same thickness ͑15 nm͒. X-ray diffractometry and sheet resistance measurements showed that the incorporation of WN x into the Ru single layer system significantly improved the barrier performance against Cu diffusion. The Ru/WN x bilayer barrier stack failed due to Cu diffusion attack after annealing at 750°C for 30 min, while the Ru single layer failed after annealing at 450°C by the formation of Cu silicide ͑Љ-Cu 3 Si͒. A high resolution transmission electron microscopy analysis clearly suggested that this was due to the excellent diffusion barrier performance of WN x film with a nanocrystalline structure embedded in an amorphous matrix.Realizing the requirement of barrier layer performance as one of the key technologies in the continuous scale-down of the integrated circuit with the Cu-based interconnect that has been highlighted in the International Technology Roadmap for Semiconductor ͑ITRS͒, 1 many efforts to enhance it have been made. They predicted that a line pitch of metal 1 should be scaled to 90 nm for a sub-50 nm technology node with the barrier thinner than 3.3 nm. 1 This requirement of the shrinkage of device size and interconnect width and thickness eventually leads to the line resistance increment due to the size effect on metal resistivity. 2 This problem can be overcome by increasing the volume of electroplated Cu filled into a trench, which can be obtained by a direct plating of Cu. 3-7 A direct plating of Cu on the diffusion barrier layer is also appealing because it reduces the technology complexity and the chance of poor conformality caused by a relatively thick sputter-deposited Cu seed layer.Materials for the direct plating of Cu were investigated to increase the volume of electroplated Cu filled into a trench. Recent investigations focused on noble materials such as Ru, Pt, Os, Rh, and Ir, and many reports suggested Ru to be successfully used as a seed layer/diffusion barrier layer for the direct plating of Cu. 3-5 Ru adheres well with Cu 8,9 and it promotes a greater Cu͑111͒ texture than Ta, 10 but Ru does not adhere well with SiO 2 and low dielectric constant materials. 11 Ru is not an effective barrier layer against Cu diffusion, and a Ru thin film with 20 nm thickness failed as a barrier layer after 450°C annealing. 8 Arunagiri et al. 12 reported that a 5 nm thick Ru thin film even failed after annealing up to 300°C. The improvement of the performance as a diffusion barrier for Cu can be made by modifying the Ru microstructure from columnar to amorphous by incorporating N into Ru during sputtering. 13 Recently, Rutransition-metal or Ru-transition-metal nitride mixed diffusion barriers have been reported. 14-17 The polycrystalline growth of Ru could be interrupted by intermixing Ru and other materials such as Ta, TaN, and WCN. In these works, plasma-enhanced...
Ruthenium ͑Ru͒ thin films were successfully grown on the TiN substrate using plasma enhanced atomic layer deposition ͑PEALD͒ by using a zero metal valence precursor, IMBCHRu ͓͑6-1-Isopropyl-4-MethylBenzene͒͑4-CycloHexa-1,3-diene͒ Ruthe-nium͑0͔͒ and direct plasma of ammonia ͑NH 3 ͒ as a reactant at the substrate temperature ranging from 140 and 400°C. The wide atomic layer deposition ͑ALD͒ temperature window from 225 to 400°C was shown and a high growth rate of 0.094 nm/cycle at the ALD temperature window was obtained, which is twice that of PEALD Ru results deposited by Cp ͑Cyclopentaldienyl͒-based Ru precursors previously reported. No incubation cycle for the growth on the TiN underlayer was observed, indicating the fast nucleation of Ru. The PEALD-Ru films formed polycrystalline and columnar grain structures with a hexagonal-close-packed phase that was confirmed by X-ray diffractometry and transmission electron microscopy analysis. Its resistivity was dependent on the microstructural features characterized by grain size and crystallinity as well as its density, which could be controlled by varying the deposition parameters such as deposition temperature and reactant pulsing condition. Resistivity of ϳ12 ⍀ cm was obtained at the deposition temperature as low as 225°C by optimizing ͑NH 3 ͒ plasma power and pulsing time.
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