The influence of incorporated nitrogen on the thermal stability of amorphous HfO2 and Hf silicate

Abstract

We investigated the thermal stability of a N-incorporated amorphous Hf silicate film in terms of Hf diffusion in the film using high-angle annular-dark-field scanning transmission electron microscopy. We first examined HfxSi1−xO2 (x=0.5,1.0) films with and without N incorporation. Our analysis showed that N incorporation (15at.% of N) into the Hf0.5Si0.5O2 film significantly suppressed chemical component separation during annealing at 1000°C. In contrast, clear separation of Hf-rich and Hf-poor (SiO2-rich) regions occurred in the Hf0.5Si0.5O2 film without N incorporation. In addition, HfO2 crystalline particle formation was observed in the HfO2 films with and without N incorporation (25at.% of N). These results strongly suggest that Si–N bonding in the N-incorporated Hf0.5Si0.5O2 film, rather than Hf–N chemical bonding, is the main cause of the suppression of the chemical component separation and HfO2 crystallization. Second, we examined Hf diffusion in a SiO2 film with and without N incorporation and found that the N incorporation significantly reduced the Hf diffusion. We therefore infer that the suppression of the chemical component separation in the N-incorporated Hf silicate film can be explained in terms of the suppression of Hf diffusion by the Si–O, N network in the N-incorporated Hf silicate film.