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

Abstract
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.