Compositional and structural changes in TiB 2 films induced by bias, in situ and post-deposition annealing, respectively

Abstract

Structural changes in TiB 2 films were induced at relatively low temperatures by the application of bias and in situ annealing or by post-deposition heat treatment of samples subjected to bias with simultaneous in situ annealing. In situ annealing by itself evoked only partial crystallization. Application of bias by itself only modified the composition of the as deposited film. A simple model is presented to explain the variation of the composition when RF bias is applied to a cold substrate. The crystallized films had a (0 0 0 1) texture. A model has been suggested to explain the observed preferred orientation, based on the contribution of surface and strain energies. Both, the surface energy and strain energy are direction dependent. These were evaluated for two film orientations reported in the literature, namely, the (0 0 0 1) and ( 1 0 1 ¯ 1 ) orientations. The preferred orientation of the film is determined by the lowest overall free energy resulting from the competition between the surface energy and the strain energy on different lattice planes. The surface energy is not film thickness dependent while the strain energy is thickness dependent and increases with it. For small film thickness, as in this work, the surface energy term is significant and (0 0 0 1) orientation with a minimum surface energy is preferred. At large film thicknesses the strain energy becomes dominant and the ( 1 0 1 ¯ 1 ) preferred orientation is observed. Under certain experimental conditions strain energy effects may tip the preferred orientation to ( 1 0 1 ¯ 1 ) . The elastic moduli in the (0 0 0 1) and ( 1 0 1 ¯ 1 ) directions were determined as 435 and 538 GPa, respectively.