Thermal stability of high-k Si-rich HfO2 layers grown by RF magnetron sputtering

The microstructure and optical properties of HfSiO films fabricated by RF magnetron sputtering were studied by means of x-ray diffraction, transmission electron microscopy, spectroscopic ellipsometry and attenuated total reflection infrared spectroscopy versus annealing treatment. It was shown that silicon incorporation in the HfO2 matrix plays an important role in the structure stability of the layers. Thus, the increase of the annealing temperature up to 1000 deg. C did not lead to the crystallization of the films. The evolution of the chemical composition as well as a decrease of the density of the films was attributed to the phase separation of HfSiO on HfO2 and SiO2 phases in the film. An annealing at 1000-1100 deg. C results in the formation of the multilayer Si-rich/Hf-rich structure and was explained by a surface-directed spinodal decomposition. The formation of the stable tetragonal structure of HfO2 phase was shown upon annealing treatment at 1100 deg. C.