Effects of High Temperature Hydrogen Annealing on n-Channel Si-Gate MNOS Devices

Abstract

High temperature hydrogen annealing, rather than high temperature nitrogen annealing, is adopted as an essential technology for fabrication of n-channel silicon-gate MNOS memory devices offering excellent charge retention characteristics. Retention is greatly influenced by the annealing ambient and temperature after nitride deposition. In case of annealing in nitrogen or oxygen, higher temperatures cause a large amount of retention degradation, while in hydrogen, they do not degrade but improve retention. The high temperature hydrogen annealing decreases both Si–SiO2 interface state density and the Si3N4 conductivity. The interface state density greatly influences charge decay due to direct tunneling when the devices are tested at room temperature. The conductivity is influential at elevated temperatures. Long retentivity is evaluated and the results confirm a ten year nonvolatility at 125°C.