The effect of composition and exposure to external factors on the electronic structure of amorphous silicon nitride in memory devices

Abstract

Silicon nitride is widely used in microelectronics as a charge storage layer in MNOS memory devices. It has been studied using soft X-ray emission spectroscopy. To understand fatigue phenomena in memory devices and the nature of localized states (LS) in the band gap, L 2,3 spectra of the valence band (VB) were obtained with attention being paid to the density of LS. a-SiN x and a-SiNx:H samples have been prepared by various methods. They were subjected to an electric field and to ultraviolet irradiation to model the degradation of devices. The investigation of a-SiN x showed that VB and especially LS spectra are very sensitive to composition changes. Increasing the nitrogen content of a-SiN x and a-SiN x:H causes a shift in the LS-spectrum to E c and separation of the maximum into two, as well as changes in the shape of the VB spectrum. It has been found that E field exposure and UV irradiation irradiation the formation of some new SiO bonds in the VB spectrum of SiN x with a shift of the main maximum of the LS spectrum to E c.