Post annealing effect on ultra-thin Hf-based high-k gate oxides on Si

We investigated the effect of post annealing on the electrical and physical properties of atomic-layer-deposited thin HfO2, HfSixOy and HfOyNz gate oxide films on Si. It was found that the main leakage conduction of all Hf-based oxide films was of the Poole–Frenkel (P–F) type in low electric fields and Fowler–Nordheim (F–N) conduction in higher fields. Also, it was observed that the transition from P–F to F–N of the annealed HfOyNz sample occurred earlier than that of the as-grown one. By using spectroscopic ellipsometry, it was found that the annealing process decreased the band gap of HfO2, HfSixOy and HfOyNz films. From depth profile measurements on the HfOyNz film, we conclude that N moves toward the surface and interface during annealing.