Competing Initial Reactions at Transition-Metal/Silicon Interfaces
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of surlace analytical tools. Interfacial silicide growth is normally activated by annealing of the metal/Si contact, with temperatures required for silicide growth being relatively low (_< 40 0 0C) for 0 icar-noble transition metals and considerably higher (> 50 (C) for refractory transition metals. Growth of silicide compounds to thicknesses of hundreds or thousands of A involves consumption (lf both metal and Si species by a growing silicide interlayer, such that the moving silicide/Si interface remains relatively uniform and approximately planar. Howeser, prominent aspects of transition-metal/Si interfacial reactivity have been found toCde\iate considerably 12,31 from the simple picture of interfacial silicide compound formation, particularly at relatively low reaction temperatures. 14,5 In these situations, other competing material reaction paths dominate kinetically over the process of simple interfacial silicidc compound forniation. These material reactions owher than ioerfacialsilicide formation have been observed in two situations. First, such material reaction at low temperature dominates the behavior of a variety of buried mietal/Si interfaces, particularly for refractory metals (e.g., Ti/Si 12,3,61 and V/Si 171). Seeond, important material reaction is observed during low temperature deposition of transition metals on Si eg..Ni/Si 11, Ti/Si 91, Pt/Si 110], and Cr/SiI 111). These material reactions likely involve 'rain boundary and surface diffusion processes respectively, which lead to reaction along a complex network of boundaries and surfaces. In this paper we review the different regtimes of chemical reaction at transition-iietal/Si interfaces. with emphasis on the reaction behavior at low temperatures where other competing material reaction paths often dominate over interfacial silicide compound formation. These aspects arc particularly important in that the low temperature reactions are initiated first in any annealing treatment.
Mat. Res. Soc. Symp. Proc. Vol. 54. 1986 Materials Research Society
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INTERFACIAL SILICIDE GROWTH The stages of interfacial silicide growth, resulting in formation of silicide compounds by contact
reaction, are depicted schematically in Fig. 1. First, unreacted metal is deposited on the Si surface, as shown in Fig. ha. With sufficient thermal energy, typically generated by annealing processes, a thin interlayer of silicide compound is produced, as seen in Fig. lb. This initial interlayer then grows thicker as metal and/or Si is consumed (Fig. hc). Finally, one of the reactant species (the metal for most silicidc applications of interest) is fully consumed and the reaction is complete (Fig. Id). The process of silicide growth, as represented by Figs. ha, hc, and Id, has been extensively studied by thin filti deposition and analysis techniques [1h, including especially x-ray diffraction, transmission electron microscopy (flat-on mode), and Rutherford backscattering spectroscopy. Since these methods usually involve limited depth sensitivity (- 100 A), the initial stage of
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