Influence of a high-temperature hydrogen anneal on the memory characteristics of p-channel MNOS transistors

Abstract

The effects of a postnitridation high‐temperature hydrogen anneal on p‐channel metal‐nitride‐oxide‐semiconductor (MNOS) memory transistors have been studied. It is shown that, although the density of surface states at the Si‐SiO₂ interface decreases with increasing temperatures, anneal temperatures exceeding the nitride deposition temperature should not be used, since they result in a nitride degradation. Short anneals at 800 °C result in a 30% reduction in the threshold voltage decay rates by elimination of backtunneling of stored charges towards the interface states. At the same time the hydrogen anneal technique guarantees a more reliable operation of transistors in the memory array and strongly increases the channel mobilities. In hydrogen‐annealed MNOS transistors the degradation process is retarded resulting in better endurance figures.