Interface state densities for metal-nitride-oxide-silicon devices

Abstract

The interface state density of metal-nitride-oxide-silicon (MNOS) devices was investigated as a function of silicon nitride (Si3N4) deposition temperature and postdeposition annealing conditions. The interface state density around the midgap of the oxide-silicon interface of the MNOS structures as a function of deposition temperature between 650 to 850 °C increased from 1.1 to 8.2×1011 cm−2 eV−1, for as-deposited silicon nitride films,; but decreased from 5.0 to 3.5×1011 cm−2 eV−1, for films annealed in nitrogen at 900 °C for 60 min; and further decreased and remained constant at 1.5×1011 cm−2 eV−1, for films which were further annealed in hydrogen at 900 °C for an additional 60 min. The interface state density increase is due to an increase in the loss of hydrogen at the interfacial region and also due to an increase in the thermal stress caused by differences in thermal expansion coefficients of silicon nitride and silicon dioxide films at higher deposition temperatures. The interface state density is subject to two opposing influences; an increase by thermal stress, and a reduction by hydrogen compensation of these states. Thus either low-temperature processing or subsequent hydrogen annealing after high processing temperatures is warranted.