Metal Silicides Formed by Direct Ion Beam Deposition

Abstract

ABSTRACTThin films of transition metal silicides have been produced at low temperatures on Si substrates by direct ion beam deposition (IBD) of the metal ion. Using a mass-analyzed beam of metallic ions rastered over the target at energies on the order of 100 eV and at substrate temperatures near 500°C, stoichiometric silicide films of varying thicknesses up to 300 nm have been formed on both n- and p-type Si. The advantages of this technique over other methods for silicide formation include good control of thickness by current integration, high purity due to the mass analysis, and control of incident ion energy which permits formation of the disilicide phase at low temperatures, thereby minimizing the thermal budget and the associated dopant diffusion in the underlying substrate. Films were characterized by Rutherford backscattering, transmission electron microscopy, and electrical measurements. Co, Fe, Ni, Ti, and W silicides have been formed by this direct deposition process. The effectiveness of the technique has been found to be dependent upon the diffusion characteristics of the particular metal/Si couple involved, with systems in which Si is the dominant diffuser, such as Ti/Si, giving the best results. Stoichiometric TiSi2 films produced at 550°C by this process show low bulk-like resistivity (15 μΩ-cm) without subsequent high-temperature annealing. All of these characteristics make silicide formation by IBD attractive for integrated circuit fabrication and shallow junction technology.