Structural investigations in the formation of the epitaxial CoSi2 layer using a Co/TiSix bilayer on Si (1 0 0)

Epitaxial cobalt silicide layers were formed on the p-type Si (1 0 0) by co-sputtering of Ti and Si as the interlayer, using the Co/TiSix bilayer structure and subsequent rapid thermal annealing (RTA) at high temperatures. The cobalt silicide films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), transmission electron microscopy (TEM) and atomic emission spectrometry (AES) to identify the phases, surface and interface morphologies and the chemical compositions. The XRD analysis results show that the epitaxial CoSi2 layer with a (2 0 0) crystallographic orientation has been successfully grown on the Si (1 0 0) substrate. Effects of the variation of the d.c. power of the sputtering process and the annealing temperature (up to 800 °C) during RTA were investigated. The presence of a Co–Ti–O spinel phase was detected during silicidation in the annealing temperature range 400–600 °C. The AFM micrographs of the surface of the annealed Co/TiSix bilayer structure show that the RMS roughness increased sharply up to 600 °C and stabilized thereafter at a moderate value of 8.9 nm, implying the formation of a relatively smoother surface in spite of high-temperature annealing. The AES analysis results indicate that native oxide on the Si substrate are removed by Ti at the beginning of RTA and Co diffuses to the clean surface of the Si substrate so that an epitaxial CoSi2 layer can form. The cross-sectional high-resolution transmission electron microscopy (HRTEM) analysis further reveals the epitaxial relationship between the CoSi2 layer and the Si (1 0 0) substrate.