XPS and HRTEM characterization of cobalt-nickel silicide thin films

We studied by X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM) films of Co-Ni/p-Si deposited by PLD on Si(100) substrates. They were thermally treated in vacuum to promote silicide formation. By means of XPS in-depth profiles, it was observed that the deposited metal film contains more Co than Ni. The Co and Ni 2p transitions present shifts characteristic of silicide at respective ranges of 778.3-778.6 and 853.2-853.6 eV, while the Si2p transition appears at 99.2-99.5 eV, as determined by XPS. By means of HRTEM, nanocrystalline regions belonging to CoSi2, Ni2Si and NiSi2 structures were identified. Some grains of CoSi2 are large in size, more than 20 nm in diameter, while Ni2Si and NiSi2 nanocrystals are of the order of 10 nm. There are several regions where no crystalline ordering seems to be apparent. The SiO2 layer acted as an effective diffusion barrier suppressing mobility of metal into the Si(100) substrate. The observed tendencies of the Co and Ni concentrations as a function of depth agree with a model of CoSi and NiSi structure separation and subsequent formation of CoSi2 and NiSi2. (C) 2000 Elsevier Science B.V. All rights reserved.