PHASE STABILITIES AND SURFACE MORPHOLOGIES OF (TI1-XZRX)SI-2 THIN-FILMS ON SI(100)

The effects of zirconium content on the phase stabilities and the surface morphologies of Ti-Zr alloy disilicide thin films were examined. The (Ti1-xZrx)Si-2 thin films were grown by codeposition of Ti and Zr alloys (200 Angstrom) onto Si(100) surfaces in ultrahigh vacuum and followed by in situ thermal annealing at temperatures between 650 and 1000 degrees C. The structural properties of films were studied by in situ Raman scattering experiments and ex situ x-ray diffraction experiments. The (Ti1-xZrx)Si-2 films with low Zr contents (x<0.1) initially form a base-centered orthorhombic structure (C49 phase) and transform to a face-centered orthorhombic structure (C54 phase) at higher temperatures. The C49-to-C54 phase transition temperature increases with increasing Zr content. When the Zr content, x, is higher than 0.1, the C49 phase is stable in the temperature range of 700-1000 degrees C, and the C49-to-C54 phase transition is not observed. We propose that increasing the Zr content in the alloy silicide films results in a decreased enthalpy difference between these two crystalline structures. An analysis based on the classical theory of nucleation indicates that the nucleation energy barrier for the formation of a C54 cluster is increased. The surface morphologies of the alloy disilicide films were studied using scanning electron microscopy, and the surface roughnesses were quantified using atomic force microscopy. Substrate coverages of the C49 (Ti1-xZrx)Si-2 thin films on Si are larger compared to the C54 TiSi2 thin films with the same thicknesses. The agglomeration of the C49 alloy silicide thin films is less severe than for the C54 TiSi2 thin films, because the C49 (Ti1-xZrx)Si-2 silicide thin films have lower surface and interface free energies than C54 TiSi2. (C) 1995 American Institute of Physics.