Thermal stability of Hf-based high-k dielectric films on silicon for advanced CMOS devices

HfSiON and HfSiO films deposited on Si(1 0 0) by reactive sputtering followed by UV/ozone oxidation were submitted to different sequential rapid thermal annealings in N2 and/or O2 atmospheres. The thermal stability of the system was addressed by determining the atomic transport and exchange of the involved chemical species using nuclear reaction analysis, nuclear resonance profiling and X-ray photoelectron spectroscopy. We investigated the effects of pre-annealing in N2 prior to O2 annealing, which leads to a decrease in oxygen diffusivity through the films. This effect was also observed in a thermal annealed HfSiO/HfSiO15N/Si structure, where the nitrogenous species present only in the intermediate layer stops the oxygen diffusion. Film growth was observed in both HfSiO and HfSiON samples. The growth is due to oxygen incorporated during thermal annealings that reacts with substrate-Si. Annealing in 15N2 promotes nitrogen incorporation only in HfSiON samples, indicating an incorporation mechanism based on isotopic exchange between 14N and 15N. We observed by XPS that the incorporated oxygen is changing the chemical environment of the film.