Defect characterization of crystalline metal oxides and high-k films by means of positron annihilation

Point defects introduced by homoepitaxial growth of thin films on SrTiO₃ substrates were studied by means of positron annihilation. The SrTiO₃ films were grown by molecular-beam epitaxy (MBE) without using an oxidant. The line-shape parameter S was found to be increased by the growth of the film, which was attributed to the diffusion of oxygen from the substrate into the film, and the resultant introduction of oxygen vacancies. The impact of nitridation on open volumes in thin HfSiO_x films fabricated on Si by atomic layer deposition was also studied. After plasma nitridation, the size of open volumes in the films decreased. An expansion of open volumes, however, was observed after post-nitridation annealing. The change in the size of open volumes was attributed to the trapping of nitrogen by such regions, and an incorporation of nitrogen into the amorphous matrix of HfSiO_x. We will demonstrate that the positron annihilation technique is a useful tool for studies of vacancies and open volumes in metal oxides.