We have systematically examined nitrogen-rich silicon oxynitrides with a thickness of about 2 nm grown by rapid thermal nitridation in ammonia. In this paper the nitrogen incorporation as well as the electrical properties of the oxynitrides are discussed in detail. With the help of elastic recoil detection measurements it could be shown that the incorporated nitrogen concentration can be controlled precisely in a range between 20 and 60%, which means that even pure silicon nitride can be thermally grown in ammonia. Depending on the process flow it is also possible to adjust the nitrogen and oxygen profiles across the dielectrics depth. Regarding the electrical properties of the grown oxynitrides, we examined the impact of the variation of the process parameters and the impact of postnitridation anneals. It was found that the dilution of the process gas ammonia by the inert gas argon has a big impact on the quality of the dielectric. The optimized oxynitrides show leakage current densities which are significantly reduced compared to that of SiO2, but their interface quality is not sufficient for metal oxide semiconductor (MOS) applications. In order to reduce the interface state density D-it, a short reoxidation in steam atmosphere combined with an anneal in forming gas results in oxynitrides with D-it values of 10(11) eV(-1) cm(-2). It is shown that for an equivalent oxide thickness of 1.3-1.5 nm, the leakage current densities are four orders of magnitude below that of SiO2 with the same thickness. Promising measurements of the effective electron mobility show that the presented oxynitrides are suitable as gate dielectrics in MOS applications in spite of the high nitrogen concentration of more than 25%. (c) 2005 The Electrochemical Society.