Optimization of sub 3 nm gate dielectrics grown by rapid thermal oxidation in a nitric oxide ambient

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 using QBD, 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 O2 have a similar effect. It is found that an improvement in reliability can be obtained by reoxidation in an N2O ambient. Surprisingly, reoxidizing in N2O proceeds at a higher rate than in O2 and this enables the use of lower thermal budgets.