Interfacial reactions between ultra-thin Ni-layer and clean 6H-SiC(0 0 0 1) surface

Abstract

The interfacial reactions between an ultra-thin (5–20 ML) Ni-layer and a clean 6H-SiC(0 0 0 1) surface were analyzed in situ by high-resolution medium energy ion scattering (MEIS), reflection high-energy electron diffraction (RHEED), and photoelectron spectroscopy using synchrotron-radiation-light. The surface morphology was observed ex situ by an atomic force microscope. It is found that the growth mode dependent on annealing temperature is basically similar for Ni-coverage above 5 ML (1 ML for 6H-SiC(0 0 0 1): 1.21 × 10 15 atoms/cm 2). Uniform Ni(1 1 1) layers grow epitaxially at room temperature and up to 450 °C in spite of a large lattice mismatch of 20%. MEIS and Si 2p core level analyses show that silicidation takes place above a critical temperature T C dependent on Ni-coverage. For Ni-coverage of 10 ML, annealing at 500 °C leads to growth of almost uniform polycrystal Ni-silicide layer with an average composition of Ni/Si ≅ 3/1 and at a higher temperature of 600 °C Ni-silicide islands are formed. The higher the annealing temperature, the islands become the more Si-rich and the larger the island height. The dispersion of the valence band spectra shows formation of a crystalline graphite layer on the top surface in the region surrounding the islands. Bond-breaking of Si–C caused by Ni–Si bonding supplies carbon atoms to form a c-axis-oriented graphite double-layer, which is quite similar to a highly oriented pyrolytic graphite.