Nitridation and post-nitridation anneals of SiO2 for ultrathin dielectrics

A technique of post-oxidation annealing to improve the properties and long-term reliability of ultrathin (<100 Å) MOS gate dielectrics is discussed. In this technique, after oxidation, nitridation is done in NH₃, followed by a light reoxidation in O₂, and then an inert anneal in Ar or N₂. Using this technique, both optimum performance and reliability can be obtained without sacrificing either. NH₃ anneal of SiO₂ improved the hot-electron immunity, but degraded the interface quality. Good properties could be obtained by a strong reoxidation of the nitrided films, at the expense, however, of a substantial increase in the film thickness. Nitrogen and argon ambients were found to be equally effective at improving film properties. By annealing the film in an inert ambient following reoxidation of the nitroxide, fixed charge can be further decreased with little oxide grown, electron mobility in NMOS FETs increases further, and the hot-electron lifetime is much longer than that of the starting oxide