The vertical scaling of oxide thickness in the ultra large scale integrated era places stringent requirements on oxide quality. In this letter we report optimization studies in the growth of ultrathin oxynitrides in the sub 3 nm range. The oxynitride growth technique used involved self-limiting growth in nitric oxide (NO) followed by reoxidation in oxygen or nitrous oxide(N2O)ambient. This method allows tight control of oxide thickness and resulted in consistently low leakage currents over a range of thicknesses from 2 to 3 nm. The reliability of the oxynitrides is characterized usingQBD,stress-induced leakage and surface charge and contact potential difference measurements. Charge-to-breakdown(QBD)data indicate that the reliability of the oxide degrades with increasing nitridation times in an NO ambient. Increasing reoxidation times in O2have a similar effect. It is found that an improvement in reliability can be obtained by reoxidation in anN2Oambient. Surprisingly, reoxidizing inN2Oproceeds at a higher rate than in O2and this enables the use of lower thermal budgets. ©1997 American Institute of Physics.