Al2O3 has been grown by Atomic Layer Chemical Vapour Deposition (ALCVD) on ntype 4H-SiC using O3 as an oxidant and tri-methyl-aluminum (TMA) as a precursor. After deposition, annealing at 1000°C during 3h in different atmospheres (Ar, N2 and O2) was performed. Interface properties were studied by Capacitance-Voltage (CV) and Thermal Dielectric Relaxation Current (TDRC) measurements. The highest near-interface trap density (Nit) was deduced to be 4x1012 eV-1cm-2 between 0.36 eV and 0.5 eV below the conduction band, Ec, for O2 annealed samples, 2.8x1012 eV-1cm-2 between 0.42 eV and 0.56 eV below Ec for Ar annealed samples and 2.2x1012 eV-1cm-2 between 0.4 eV and 0.6 eV below Ec for N2 annealed samples. Only samples annealed in Ar exhibit a nearly trap free region close to Ec. Annealing in N2 is found to decrease Nit between 0.3 and 0.7 eV but shows a slightly higher Nit close the conduction band compared to the Ar case.