A kinetic model for silicide formation through solid state reactions in metal-silicon diffusion couples

In this study, a kinetic model for silicide formation through solid state reactions in transition metal-Si diffusion couples has been developed. The reactive interface in a metal-silicon couple is considered to be a reaction region, and the reaction process is divided into three steps. Several physical quantities have been defined to describe each of these steps, i.e., the diffusion flux of moving reactant to the reaction region (J), the release rate of nonmoving reactant (r) and the formation rate of the growing phase (F). The relationship between these quantities in a given reaction region has been demonstrated by means of a reaction process plot (RPP), which is also developed in this study.; Expressions for free energy degradation rate (FEDR) in a reaction region are derived. It is shown, by using the expressions and an RPP, that in a given reaction region there are always a number of possible reaction processes competing with one another. One of these processes can result in the largest FEDR. Based on this result, a criterion for solid state reactions in metal-Si diffusion couples is proposed, i.e., of all possible reaction processes, the reaction which can result in the largest FEDR will actually occur.; According to the kinetic model and the reaction criterion, the stepped curve in the RPP for a reaction region adjacent to an elemental nonmoving reactant represents the actual reaction path of the release process in the region. Therefore, the silicide formation sequence in the region is predictable if the stepped curve or the RPP for the region is available. A method for calculating relative maximum release (RMR) rates and constructing semiquantitative RPPs (SRPPs) has been proposed. Using this method, calculations of RMR rates have been done for 15 metal-Si systems and a few typical SRPPs have been drawn using the resulting data. Predictions of first silicide formation and multiple phase growth sequence have been done using the SRPPs for these systems. Comparison of the predictions with the experimental results from the literature shows very good agreement, which provides strong support for the kinetic model and the reaction criterion.; Multiple phase sequential growth in thin film Ni-Si couples has been investigated by means of transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDS) and electron diffraction. The observed growth sequence is Ni{dollar}sb2{dollar}Si and then NiSi. Experimental results from a previous study using thin film Mn-Si couples are also given, which indicates a formation sequence of Mn{dollar}sb3{dollar}Si followed by MnSi. The results in the two systems provide experimental evidence for the predictions of silicide formation sequences in these systems.; Direct deposition reactions of Ni on Si substrates have also been investigated using TEM, EDX and electron diffraction. The observed silicide formation sequence is NiSi{dollar}sb2{dollar}, Ni{dollar}sb2{dollar}Si, then NiSi and Ni-rich solid solution layers. Most of the observed phenomena in this study can be explained by SRPPs and the new kinetic model, which provides additional support for the new model.