Structural properties of nickel silicided Si_1-xGe_x(001) layers

We have investigated the interfacial reactions of Ni films on Si_1-xGe_x (x = 0.0-0.2) epitaxial (001) layers as a function of the annealing temperature between 300 and 800°C. It is shown that the Ni-silicided Si_1-xGe_x layers have a higher sheet resistance and poorer surface and interface morphologies, compared to the Ni-silicided Si layer. As the annealing temperature is increased, the silicide layers become irregular with thermal grooving and, consequently, become agglomerated. This is more severe in the sample with a higher Ge content. Glancing angle x-ray diffraction results show that, unlike the Ni-silicided Si sample, for the Si_1-xGe_x (x = 0.1 and 0.2) samples, no phase transition from Ni germanosilicide (Ni(Si_1-mGe_m)) to Ni(Si_1-nGe_n)₂ occurs throughout the annealing temperature domain. Transmission electron microscopy and energy dispersive spectroscopy results show that Ge atoms outdiffuse from the Ni germanosilicide as the annealing temperature increases. The outdiffused Ge atoms are segregated at the Ni germanosilicide/Si_1-xGe_x interfaces and at the surface regions between the agglomerated germanosilicide. A simple model is given to describe the Ge segregation and silicide islanding behaviours.