A new Cu(NbCNx) film and some of its characteristics

Abstract

In this study, a new type of 8 or 300 nm-thick Cu(NbCNx) alloy films is created via barrierless Cu metallization by co-sputtering copper (Cu), niobium (Nb) and carbon (C) on silicon (Si) substrates within an Ar or Ar/N2 vacuum charmer. Various composition sets were explored in search of an optimal set for the new film to achieve a lowest possible resistivity. The resistivity values of pure Cu, Cu(NbC) and the new films after isothermally and cyclically annealing at various temperatures were respectively measured and analyzed. The XRD patterns of the new films and Cu(NbC) films indicate that NbCNx and NbC phases discretely exist, that no compounds are formed by any interactions among Cu, Nb, and C, and that solidly-dissolved NbCNx and NbC phases can, respectively, boost the thermal stability of the films up to 710 and 600 °C. Owing to the within NbCNx solid solution that helps avert oxidation, the new film's electrical stability, hence, becomes superior to its pure Cu counterpart. The cross-sectional transmission electron microscope (TEM) images of the annealed new film are examined and discussed. The new film exhibits 10-year projected reliability up to 1MV/cm, which is confirmed by its time-dependent dielectric-breakdown (TDDB) lifetime vs. electric strength curves plotted in the study. The X-ray diffraction (XRD) patterns of an Sn/Cu(NbCNx)/Si structure taken in the study fortify that the new film's enhanced thermal stability is caused by NbCNx formed within. Main causes that improve the thermal stability and anti-oxidation capability of the new film are also analyzed. The cross-sectional TEM images of an Sn/Cu(NbCNx)/Si structure reveal the existence of a 2.56 Å d-spacing NbCNx phase and the full suppression effect on CuSn interaction by the phase. The adhesion strength of a 300 nm-thick, as-deposited new film on an Si substrate is 6 to 7 times that of a pure Cu film and, after being annealed at 600 °C for 1 h, grows to 11 to 12 times that of said pure Cu film, as concluded by the adhesion test results in the study. Even after the film thickness is reduced to 8 nm, the new alloy film's adhesion strength remains at a comparably high level. The mentioned merits seem to make the new film a good candidate material for several industrial applications, e.g., in-circuit printing and interconnect making.