In addition to the previously proposed in situ pyrolytic-gas passivation (PGP) using N2O, PGP using NF3 was simultaneously performed. As a result, a synergistic effect of passivation for ultrathin silicon oxide films was confirmed. That is, the potential barrier height energy of the oxide and the interface state density were significantly improved. This was probably caused by the microscopic structural change in the oxide near the interface due to quantitative analyses of F and N. It is also believed that F passivation effectively contributes to compensate the inconsistent-state bonding sites near the interface that remain with N passivation. (c) 2006 The Electrochemical Society.