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In this paper, the diffusivities of copper in 15 nm thick Ru and Ru–C barrier layers are determined experimentally by using sheet resistance and X-ray diffraction measurements with the Cu/barrier/Si samples. By fitting the dependence of diffusivities on temperature, the activation energy for Cu diffusion in Ru–C film is 1.11 eV, which is substantially higher than that in Ru film _0.54 eV_. Microstructural analysis by transmission electron microscopy combined with energy-dispersive X-ray suggests that the higher activation energy for Cu diffusion in Ru–C is associated with the stuffing of added carbon atoms on the grain boundaries of the Ru matrix and consequently leading to the superior diffusion barrier performance of the Ru–C film. © 2010 The Electrochemical Society. _DOI: 10.1149/1.3479383_ All rights reserved.

Sputtered Ru and Ru-C films 5 nm thick are employed in the Cu/barrier/SiO 2 /Si system, and their performances as the diffusion barrier as well as the seed layer for direct Cu electroplating are investigated in parallel. Based on the sheet resistance measurement and energy dispersive X-ray line profiles, the 5 nm Ru-C film can retard the diffusion of Cu after a prolonged (30 min) annealing up to 700°C, while the Ru film is an effective barrier up to only 400°C. Direct electroplating of Cu is successfully carried out on both Ru and Ru-C films, which proves that Ru-C is a Cu seed layer in addition to being a robust diffusion barrier. The microstructural characteristics of ultrathin Ru and Ru-C films are also examined, indicating that the superior barrier performance of the 5 nm Ru-C film is associated with its inferior crystallinity and resistance to agglomeration at elevated temperatures.

Ru-Ta and Ru thin films (∼ 15 nm in thickness) as diffusion barrier for Cu metallization on SiO 2 /Si and Si substrates are studied. Experimental results show that the Ru-Ta film exhibits amorphous structure until annealing at 700°C, whereas the Ru film crystallizes in as-deposited and annealed states. Sheet resistances of Cu/Ru and Cu/Ru-Ta stacking layers increase after annealing at 500 and 700°C, respectively, regardless of whether the substrate is SiO 2 /Si or Si. Increase in resistance is concurrent with the formation of Ru 2 Si 3 and Cu 3 Si when Cu/barrier stacks are deposited on Si substrate. Increase in resistance for Cu/barrier stacks deposited on SiO 2 /Si substrate is related to the diffusion of Cu through the crystallized barrier to the underlayers. Furthermore, current-voltage measurement also reveals that the Cu/Ru-Ta metallization has a lower leakage current than the Cu/Ru system. The failure mechanism and the effectiveness of Ta addition on barrier performance are discussed. © 2008 The Electrochemical Society. [DOI:10.1149/1.2999348]. All rights reserved.

Ultrathin Ru-N and Ru-Ta-N films (∼ 15 nm in thickness) deposited by reactive sputtering are applied as a diffusion barrier in the Cu/bartier/SiO 2 /Si systems. After film deposition, the samples are tested before and after annealing at 200-900°C in vacuum for 30 min. The sheet resistance examined by four-point probe appraises that the Ru-Ta-N barrier would not fail until annealing at 900°C, as compared to Ru-N, which fails after annealing at 600°C. The depth distribution of elements examined by Auger electron spectroscopy confirms different degrees of Cu diffusion into underlayers for the two systems after annealing at 600°C. Also, the cross-sectional microstructures of the Cu/barrier/SiO 2 /Si samples analyzed by transmission electron microscopy, the crystallinity of barrier films examined by grazing incident angle X-ray diffraction, and the chemical state of barrier characterized by X-ray photoelectron spectroscope might explain the difference in barrier performance for the ultrathin Ru-N and Ru-Ta-N films in the Cu/barrier/SiO 2 /Si multilayered systems.

The thermal stability performance of double 8-doped In 0.42 Al 0.58 As/In 0.46 Ga 0.54 As metamorphic heterostructure field-effect transistors with Au and Ti/Au metal gates are comprehensively studied and demonstrated. By evaporating the Ti/Au metal gate, the thermal stability of device characteristics are significantly improved as compared with the device with conventional metal gate (Au). Experimentally, the device with a Ti/Au metal gate simultaneously exhibits the considerably lower temperature degradation in turn-on voltage (-2.19 mV/K), breakdown voltage (-34 mV/K), logic swing (-1.24 mV/K), transition region width (0.05 mV/K), on-off current ratio (-3.55 /K), threshold voltage (-0.25 mV/K), impact ionization-induced gate current (1.63 X 10 -3 μA/mm K), output conductance (1.23 μS/mm K), and voltage gain (-0.33 /K) as the temperature is increased from 300 to 510 K. Consequently, the studied device with a Ti/Au metal gate is a good candidate for high-speed and high-temperature digital and switching circuit applications.