Metrology study of sub 20Å oxynitride by corona-oxide-silicon (COS) and conventional C-V approaches

This work aims to develop an in-line corona-oxide-silicon (COS) monitoring strategy for the 20 Å oxynitride gate dielectrics. The oxynitride gate dielectrics were composed of ln-Situ Steam Generated oxide (ISSG) oxide at thickness of 16Å and 20Å which were exposed to Remote Plasma Nitridation (RPN) for various time durations. The nitrogen density in the oxynitride established by SIMS and nuclear reaction analysis (NRA), was correlated with the non-contact electrical measurements taken by Quantox^TM. The non-contact electrical parameters included interface trap density (D_it), flatband voltage (V_fb), total charge (Q_tot), equivalent oxide thickness (EOT) and leakage current. The pre-anneal D_it measurements exhibited a strong correlation with the nitrogen density and was the most sensitive process monitoring parameter. The V_fb and Q_tot, on the other hand, showed little correlation. The ISSG/RPN oxynitride process required further optimization because there was no significant reduction in EOT for the annealed samples. Furthermore, the leakage current in the pre-annealed samples increased with the RPN exposure possibly indicating plasma damage. Conventional MOS C-V measurements were also conducted. Similar to the Quantox^TM results, there were no reductions in EOT or current density. A comparison between the C-V and the Quantox^TM data indicated no simple linear relationship between these two techniques. Due to the limited samples used for the Quantox^TM/C-V comparison, a more extensive work is required to confirm the present observation.