XPS and HRTEM characterization of cobalt-nickel silicide thin films

We studied by X-ray photoelectron spectroscopy (XPS) and high-resolution tr ansmission electron microscopy (HRTEM) films of Co-Ni/p-Si deposited by PLD on Si(100) substrates. They were thermally treated in vacuum to promote si licide formation. By means of XPS in-depth profiles, it was observed that t he deposited metal film contains more Co than Ni. The Co and Ni 2p transiti ons 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 e V, as determined by XPS. By means of HRTEM, nanocrystalline regions belongi ng to CoSi2, Ni2Si and NiSi2 structures were identified. Some grains of CoS i2 are large in size, more than 20 nm in diameter, while Ni2Si and NiSi2 na nocrystals are of the order of 10 nm. There are several regions where no cr ystalline ordering seems to be apparent. The SiO2 layer acted as an effecti ve diffusion barrier suppressing mobility of metal into the Si(100) substra te. The observed tendencies of the Co and Ni concentrations as a function o f depth agree with a model of CoSi and NiSi structure separation and subseq uent formation of CoSi2 and NiSi2. (C) 2000 Elsevier Science B.V. All right s reserved.