Growth and characterization of Ta/Ti bi-layer films on glass and Si (1 1 1) substrates by direct current magnetron sputtering

The influence of a sputter-deposited titanium adhesion layer on glass and Si (1 1 1) substrates with or without exposure of titanium layer surface to the atmosphere on the growth mode of the tantalum films was studied. It was found that, because of the well match of the cell constants between the deposited Ta and the underlying Ti, the tantalum films continuously deposited on the adhesion layer of titanium grown without breaking vacuum always grew with the orientation following that of the bottom titanium layer and nucleated bcc α phase of tantalum with low degrees of orientation. After exposure of the bottom titanium layer surface to atmosphere, the absorption and diffusion of oxygen and other impurity atoms on the surface would promote a higher lever of oxidation and favor to form more and more titanium suboxides at the Ti surface. The increase of titanium suboxides at the Ti surface change the lattice mismatch between the underlying titanium film and the bcc-Ta film, which disturbed the nucleation of α-Ta and promoted the growth of β-Ta. Consequently, the electrical properties of the Ta/Ti bi-layer films were significantly changed.