A study of the kinetics and microstructure evolution during reactions of niobium/aluminum and titanium/aluminum multilayer thin-films

The study of phase formation kinetics and concurrent microstructure evolution in thin films is important to the development of interconnects for integrated circuits. The present work used differential scanning calorimetry (DSC), X-ray diffraction (XRD), and transmission electron microscopy (TEM) to examine aluminide formation in Nb/Al and Ti/Al thin-film multilayers with a fixed overall composition of XAl3 (X = Nb,Ti). The effects of bilayer thickness (Λ) and composition on reaction kinetics and microstructure were investigated in films with Λ = 10 nm - 333 nm composed of Al, Al-0.5 wt.% Cu and Al-1.0 wt.% Cu layers.; DSC results indicated that solute Cu was did not effect the activation energy of the formation of NbAl3. However, 1.0 wt.%Cu increased the activation energy for formation of the metastable, cubic superlattice structure of TiAl3. The Avrami exponents associated with NbAl3 and TiAl3 formation suggested the possibility of heterogeneous product phase nucleation. Finally, analysis of DSC data indicated that the formation enthalpy of NbAl3 and TiAl3 was unchanged by the presence of Cu.; XRD showed that the multilayers exhibited Al <111>/Nb <110> or Al <111>/Ti <0002> fiber texture. The fiber plot pole intensity and peak width depended on layer thickness and Cu concentration. The presence of Cu reduced the fiber texture in both types of multilayers. In situ synchrotron XRD was used to study the formation kinetics of TiAl 3 and NbAl3. Using this approach, the effective activation energies for the formation of NbAl3 as well as the metastable and equilibrium structures of TiAl3 were determined.; Cross-section TEM was used to examine the microstructures of as-deposited multilayers and samples that were annealed to different stages of the reaction. This provided a comparison with predictions of existing models of two-stage reaction kinetics. Analytical electron microscopy was used to determine the elemental distributions during the early stages of the Nb/Al reaction. Enhanced diffusion was observed at the intersections of Al grain boundaries with the Nb layer.