Study on oxynitride buffer layers in HfO2 metal-insulator-semiconductor structures for improving metal-insulator-semiconductor field-effect transistor performance

In this study, we investigate effects of various buffer layers on the electrical properties of HfO2 metal-insulator-semiconductor (MIS) structures under fixed conditions for HfO2 deposition and postdeposition annealing. The buffer layers are prepared using several processes including oxidation, oxynitridation and nitridation. The equivalent oxide thickness (EOT), the flat-band voltage and the flat-band voltage hysteresis of the HfO2 MIS structures depend on the nitrogen density per unit area in oxynitride buffer layers. We reveal that the increase of EOT due to postcleposition annealing is suppressed by a certain amount of nitrogen density in oxynitride buffer layers. Based on the results, we propose an engineering methodology for the nitrogen composition and the physical thickness of the oxynitride buffer layers so as to obtain a high-performance MIS field-effect transistors.