Tailored microstructures of niobium-niobium silicides by physical vapor deposition

The feasibility of fabricating Nb-Nb silicide microstructure by Physical Vapor Deposition with sufficient control of impurities has been investigated. It is demonstrated that electron beam evaporation can satisfy the requirement of impurity control under appropriate vacuum condition. In elemental layered structure of Nb and Si, NbSi2 is the first phase formed upon annealing. It was found that, at 600 degrees C, the growth rate of NbSi2 phase at the interface of Nb and Si is 35 angstrom/min. The Nb5Si3 phase nucleates at a higher temperature around 900 degrees C) at the interface of Nb and NbSi2. In the case of co-deposited film with overall composition around Nb5Si3, NbSi2 formation is by-passed. Thus, multilayers of Nb/NbSi2 or Nb/Nb5Si3 can be formed from layered elemental deposition and subsequent heat treatment under controlled conditions by adjusting the starting thicknesses of the films. Alternate elemental and co-deposited and subsequent or-in-situ heat treatment can directly form the layered Nb/desired silicide composite. Multilayers of Nb/NbSi2 and Nb/Nb5Si3 with layer thicknesses below 500 angstrom have been formed from layered elemental deposition