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This report studies the electromigration performance of W-plug via structures under the reservoir effect. The lifetime improvement factor M was observed to be a weak function of the stressing current and approximately equal to 2. A Simple model is included in the report to explain this observation. The model also predicts the most effective reservoir length for electromigration lifetime improvement.

The electromigration (EM) performance of W-plug via-fed lead test structures has been investigated. It was observed that the median time-to-failure (MTTF) and time-to- ailure dispersion (σ) depended on the number of vias servicing the lead. With multiple-vias feeding the metal lead, the early times-to-failure tended to be suppressed. In general, as the number of W-plug vias feeding the metal lines increases, MTTF tended to increase and σ tended to decrease. Also, the activation energy (0.85 eV) observed during this via-fed EM study is consistent with reports of interfacial diffusion.

This letter reports the effects of via current density on electromigration (EM) failure in Al–0.5 Cu conductors. Two-level metallization structures, differing in the number of feeding vias (1, 6, and 15), were made with the same pattern of Al lines at two levels to allow simultaneous EM testing of upper- and lower-level lines. It was established that the lower-level lines were more susceptible to the impact of the via, resulting in a failure by the formation of a local void beneath a via and a strong dependence of EM lifetime on the via current density. The results led to a phenomenological equation that incorporates via structure into failure kinetics.

The site preference of ternary additions in an A3B intermetallic compound with the L12 structure is modeled using the tetrahedron approximation of the Cluster Variation Method. At T = 0 K, there are three fundamental site preference behaviors for the ternary additions, depending on the relative magnitude of the effective pair interactions. It is found that the site preference of the ternary element is generally not related to the direction of the L12 solubility lobe. Our model also indicates that, under some conditions, the site preference can change with alloy composition and with temperature.

The temperature-composition phase diagram of the Ni-Cr system was calculated using a first-principles approach based on a statistical-mechanical approximation for the configurational entropy and a tigh-binding method for electronic structure calculations. A self-consistent tight-binding Hamiltonian with only d-electrons was implemented by imposing a condition of zero charge transfer. Hamiltonian parameters were taken from the results of first-principles band-structure calculations. The effects of self-consistent d-electron numbers for pure Ni and Cr on the phase diagram and thermochemical properties were also investigated.

The temperature-composition phase diagram of the NiCr system is calculated using 1. (i) a semi-empirical thermodynamic model and 2. (ii) a first principles model based on a tight-binding description of the electronic structure of the alloy. In all our calculations we use a theoretical structural energy for f.c.c. Cr that is considerably larger than previous empirical estimates. Our results indicate that the procedure of fitting experimental phase diagrams with free energy models lacks the sensitivity required for an unambiguous determination of structural energies. Good overall agreement with experimental data is obtained for both the semi-empirical and first principles models. From the calculated effective pairwise interactions we obtain the experimentally observed Pt2Mo type structure as one of the possible stable structures at 67at.% Ni.

The Cluster Variation Method is used to study metastable phase equilibrium and possible ordering reactions in the Ni2AlTi⇆;NiAl dual phase alloy system. The Cluster Variation Method was also used to model the corresponding binary alloys and the results were extrapolated to the ternary system. The occurrence of a continuous ordering reaction in the Ni-Al-Ti system is proposed and possible decomposition reactions are discussed.