Variation of the nucleated products in ultrathin films of Ti-Co on Si substrates with processing changes

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Abstract
The purpose of this study is to investigate solid-state nucleation and growth in Ti/Co/Si and Co/Ti/Si thin-film ternary systems, and to compare results under a variety of preparation conditions. The deposition methods used were rf sputtering and e-beam evaporation. The nucleated compounds are determined by transmission electron microscopy and diffraction. CoTi2 is the first nucleated compound in the Ti/Co/Si ternary systems prepared by e-beam evaporation irrespective of substrate temperature, thickness, or other factors. This is in contrast to the films produced by rf sputtering where this phase was not observed. Experimental findings also show that in thin-film ternary systems, the first-phase nucleation temperature and subsequent compounds could be altered as the intermediate metal layer becomes less than 20 Å. This is an indication that interference between interfaces begins to play a significant role at about this thickness, so that the reaction paths and the first nucleated phases are determined not only by internal binary kinetics, but also by intermediate transition metal layer restrictions in the interfacial region. In addition, a phase previously reported on Ti/Si system was also found in the Ti/Co/Si and Co/Ti/Si systems, and is labeled the (TiSi)N (metastable) phase. This phase occurs in the form of coherent precipitates of a nonequilibrium metastable structure.