The Combined Effect of Hydrogen and Oxygen Impurities in the Silicon Nitride Film of MNOS Devices

Abstract

The combined effect of varying the hydrogen and oxygen impurities in the silicon nitride film of metal‐nitride‐oxide‐semiconductor (MNOS) devices was studied to develop a correlation among the chemical composition, current conduction, charge trapping, and memory properties of the devices. The atomic percentage of hydrogen increased in the film as a function of decreasing deposition temperature from 850 to 650°C. Oxygen was incorporated into the film by replacing nitrogen atoms through the use of nitrous oxide gas during the film deposition process. The addition of oxygen further reduced the hydrogen concentration in the film. The trapped electron and hole densities decreased by 25 and 66%, respectively, with a corresponding decrease in film conductivity as hydrogen and oxygen concentration in the silicon nitride film increased by 4 and 12%, respectiyely. The incorporation of hydrogen and oxygen improved the overall average device retention and endurance characteristics by 40% and from 107 to 108 cycles, respectively. The hydrogen and oxygen impurities may passivate the silicon dangling bonds associated with shallow traps within the bandgap of silicon nitride and, thus, allow the carriers to become trapped in deep traps, yielding enhanced memory properties in the MNOS devices.

Contrasting single-wafer and batch processing for memory devices

“…It is believed that hydrogen diffusion out from the silicon nitride film due to the high DRAM thermal budget is the source for this fixed charge [5]- [7]. This out-diffusion of hydrogen occurs at relatively low temperatures of 600 C. Also, the hydrogen that is bonded to the silicon atom has been identified in the literature as the likely source in the silicon nitride films.…”