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CoSi2 and NiSi2 thin films on silicon are prototypes in the field of epitaxy, mainly because of their excellent lattice match with Si substrates, although the compatibility of these silicides with Si-based microelectronic industry has surely contributed to the large interest in these materials. Special growth methods have been developed to form high-quality epitaxial CoSi2 or NiSi2 thin films on Si. On the other hand, in this work, we focus on disilicide films grown by solid phase reaction (SPR). NiSi2 thin films grow with high epitaxial quality on the technologically relevant Si(100) substrates during SPR, while a film of CoSi2 grown by SPR has a polycrystalline character. NiSi2 (CaF2, a = 5.406Å) has a slightly larger lattice parameter than CoSi2 (CaF2, a = 5.364Å) and therefore has a smaller lattice mismatch with the Si substrate (diamond, a = 5.435Å). By alloying the CoSi2 film with Ni, we can gradually vary the lattice parameter of the mixed Co1-xNixSi2 phase and thus create an ideal system to investigate the role of the lattice parameter in the growth of epitaxial thin films.
We deposited 11 nm thick Co1-xNix metal films on Si(100) substrates. The silicide thin films were formed in a two-step RTP annealing process. After silicidation, the texture of the films was investigated using Rutherford backscattering and channelling (RBS/C), X-ray diffraction (XRD) measurements using synchrotron radiation (θ-2θ and pole figures) and electron backscatter diffraction (EBSD).
Our results show that in the development of the texture of silicide films, the lattice match within the silicide-silicon interface, i.e. epitaxy, is less important than the continuity of atomic planes across the plane of the interface, i.e. axiotaxy. For intermediate Ni concentrations (25-40% Ni) the disilicide nucleation site plays a dominant role in the texture development. For high Ni concentrations the film texture is close to that of a pure NiSi2 thin film despite the fact that the film does not nucleate at the silicide-silicon interface. The size of the grains and the strong (100) texture (i.e. high epitaxial quality) for the Ni rich compounds indicate that the kinetics of the silicide formation has a large influence on the final texture of these films. |