Annealing effects on electrical and structural properties of Al2O3 films deposited by ALD

Al2O3 films have been grown by Atomic Layer Deposition (ALD) on (i) HF-stripped silicon substrate and (ii) thermally grown 0.5 nm SiO2 interfacial layer. After post-deposition annealing at various temperatures, bulk and interface properties of the films have been studied by x-ray diffraction, fourier transform infrared spectroscopy and high resolution transmission electron rnicroscopy. It was shown that the SiO2 layer beneath Al2O3 delays the crystallization of the film and improves the interface stability. While the crystallization of Al2O3 films on HF-last silicon is found to start after annealing at 800°C for 30 min and be completed for 850°C, 15 min, uncompleted crystallization is obsewed even after 1000°C, 15 min annealing for Al2O3 films with SiO2 buffer layer. Electrical measurements show a shift of C-V characteristics ta positive voltages and an increase of defect densities with the annealing temperature. Even after complete crystallization leakage current of films rernains at low level ( <10-8/cm2 at -3 V). The Al2O3 layers annealed at 800°C for 15 min exhibit neither crystallization nor electrical degradation showing good thermal stability of Al2O3 up ta this temperature