Electrical properties of the TiSi2-Si transition region in contacts: The influence of an interposed layer of Nb

The influence of an interposed ultrathin Nb layer between Ti and Si on the silicide formation and the electrical contact between the silicide formed a nd the Si substrate is investigated. The presence of the Nb interlayer resu lts in the formation of ternary alloy (Nb,Ti)Si-2 in the C40 crystallograph ic structure adjacent to the Si substrate. Depending on the nature of the S i substrates and/or the amount of the initial Nb, the interfacial C40 (Nb,T i)Si-2 leads, in turn, to either epitaxial growth of a highly faulted metas table C40 TiSi2 or formation of the desired C54 TiSi2 at a lower temperatur e than needed for it to form in reference samples with Ti deposited directl y on Si. On p-type substrates doped to various concentrations, the Nb also leads to a considerably lower specific contact resistivity than that obtain ed in the reference samples: a twofold to fourfold reduction in the contact resistivity is found using cross-bridge Kelvin structures in combination w ith two-dimensional numerical simulation. As C40 (Nb,Ti)Si-2 forms at the i nterface when an interfacial Nb is present, the interface characterized is likely to represent the one between (Nb,Ti)Si-2 and Si. For the reference s amples, the interface studied is between TiSi2 and Si. (C) 2001 American In stitute of Physics.