Annealing of Al2O3 thin films prepared by atomic layer deposition

Amorphous Al2O3 thin films were deposited on a Si ( 1 1 1) substrate at 150 degrees C in oxygen-rich conditions by atomic layer deposition. Rapid thermal annealing was performed at high temperatures, ranging from 1000 to 1200 degrees C, to study the crystallization characteristics of the Al2O3 films. X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy, atomic force microscopy and frequency-dependent capacitance measurements were used to characterize the structural and electrical properties before and after the annealing. It was found that the best crystallization of the Al2O3 film was achieved after annealing at 1150 degrees C, corresponding to a minimum of full width at half maximum (FWHM) of the Al2O3 (012) XRD peak and the maximum of surface roughness and the capacitances. This suggests that 1150 degrees C is the optimal transition temperature from amorphous to crystalline and to get the best insulating property for Al2O3 thin film. The formation of the SiO2 interfacial layer after annealing has been observed by HRTEM for the annealed sample, accompanied by a decrease in the thickness of Al2O3 films.