We report on the basis of Cu-NQR measurements that the ground state in a series of Ce x Cu 2 Si 2 compounds evolves from a magnetically ordered phase at x 0.975 to a heavy-electron superconducting (SC) phase at x 1.025. We have found that the sample of x 0.99 does not exhibit any trace of magnetic phase transition down to 0.012 K. Slow magnetic fluctuations with low frequencies comparable to the NQR frequency develop rapidly below T m ϳ 1.2 K. This unusual "critical magnetic phase" can coexist with the SC phase. For the samples of x 1.00 and 1.025 such a state is expelled by the onset of the SC state. [S0031-9007(99)

We report Cu NQR results on Ge-doped heavy-fermion superconductors CeCu 2 (Si 1Ϫx Ge x ) 2 (0Ͻxр0.2) and compare with previous results on Ce 0.99 Cu 2.02 Si 2 (xϭ0). Once only 1% Ge is substituted for Si to expand the lattice, an antiferromagnetic ͑AFM͒ order sets in at T N ϳ0.7 K, followed by the onset of superconductivity at T c ϭ0.5 K. The sudden emergence of AFM order due to the slight Ge doping reinforces that an exotic magnetic phase at xϭ0 is in fact a marginal AFM state where slowly fluctuating AFM waves propagate over a long distance. The appearance of internal fields throughout the sample that is deduced from the NQR spectral shape below T N , excludes the presence of phase segregation between the superconducting ͑SC͒ and the AFM phases in the coexistent state below T c . The 1/T 1 result does not show significant reduction below T c , followed by a T 1 Tϭconst behavior. This indicates that the SC phase is in a gapless regime, dominated by magnetic excitations due to the coexistence of AFM and SC phase. As Ge content increases, T N is progressively increased, while T c is steeply decreased. As a result of the suppression of the slowly fluctuating AFM waves in the samples with more than xϭ0.06, their magnetic properties above T N progressively change to those in a localized regime as observed in CeCu 2 Ge 2 . The exotic interplay between magnetism and superconductivity in 0рxϽ0.06 is discussed in the context of a SO͑5͒ theory that unifies superconductivity and antiferromagnetism.

The effect of plasma treatment and a dielectric diffusion barrier on electromigration (EM) performance was examined. The characteristics and adhesion properties at the interface between copper (Cu) and the dielectric diffusion barrier were also investigated by scanning transmission electron microscopy–electron energy loss spectrometry (STEM–EELS). The existence of oxygen at the interface after hydrogen (H2) plasma treatment, which has a large pre-exponential factor, causes a large EM drift velocity. Ammonium (NH3) plasma treatment can reduce the Cu oxide completely, resulting in an improvement in EM performance. On the other hand, the dielectric diffusion barrier of SiCxNy, which has a better adhesion property then SiCx, reduces EM drift velocity and provides a larger activation energy. The reduction of CuOx completely by plasma treatment is essential and the selection of dielectric diffusion barrier is important to improve the EM performance of Cu damascene interconnects.

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