In this paper, we investigate the feasibility of SiO2/Al2O3 stack tunnel dielectric for future Flash memory generations using statistical leakage current simulations. We show that the statistical Monte Carlo (MC) simulator we employed reproduces accurately leakage currents measured on SiO2/Al2O3 dielectric capacitors. Exploiting its statistical capabilities, we calculate leakage current distributions in Flash memory retention conditions. We show that the high defectiveness of AI2O3 stacks strongly reduces the potential improvement of Flash retention due to the introduction of AI2O3 tunnel dielectric.