Local structural phase determination of Ni silicide thin films using EXAFS



The local structural characterization of novel contact materials (nickel silicides) on N2+ implanted Si(100) substrates have been performed using Extended X-ray-Absorption Fine-Structure Spectroscopy (EXAFS). The crystal phases of nickel silicides that are stabilized on Si (100) substrates (NiSi or NiSi2) upon varying implantation and post deposition annealing conditions were identified. The questions addressed are whether the final stabilized crystal phases of the nickel silicide layers could be identified and the fraction of the various crystal symmetries could be determined. The identification of the stabilized crystal phases in the nickel silicide formation process is crucial, as it was shown that a Si rich Ni silicide layer at the NiSix/Si interface causes a significant reduction in the electron Schottky barrier height (SBH). EXAFS analyses using experimental and theoretical references were performed on nickel silicide thin films on silicon substrates exposed to different N2+ ion doses prior to nickel deposition and silicidation processes. Using EXAFS analyses, the stabilized phases (e.g. NiSi vs. NiSi2, etc.) and their ratios were determined. EXAFS was proved to be sensitive to the subtle modifications of the crystal structures introduced by these modifications in the processing conditions. EXAFS analyses of the experimental reference structures (NiSi, NiSi2 powder samples) clearly exhibited the robust differences in the Fourier Transformed (FT) EXAFS data in the first shell region. EXAFS fits using theoretical structures corresponding to NiSi and NiSi2 symmetries have successfully identified the distinct crystal phases present in nickel silicide thin films subjected to different doses of N2+ ion implantation. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)