The investigation of an amorphous SiOx system for charge storage applications in nonvolatile memory at low temperature process

Beside silicon nitride, silicon rich SiOx is a good charge storage material for the charge trap type of nonvolatile memory due to the high density of the charge traps. In this study, the charge storage ability of various amorphous SiOx materials has been investigated. By controlling the ratio of N2O/SiH4 gases from a 1:6 to a 2:1 input gas flow rate, the deposited SiOx bandgap changed from 2.3 to 3.9 eV. The charge storage properties of the SiOx system were studied on metal–insulator–semiconductor structures with an insulator stack of SiO2/SiOx/SiOxNy on an n-type silicon wafer. In this structure, the SiO2 was used for the blocking layer and the SiOxNy was used for the tunneling layer. By analyzing the FTIR and the photoluminescence spectra, it is shown that the richest silicon material incorporates numerous non-bridging oxygen hole-center (NBOHC) defect sources and a rich silicon phase in the base material. These defects, as well as the amorphous silicon clusters that exist in the SiOx layer, enhanced the charge storage capacity of the device compared to the oxygen rich SiOx cases. The retention property was optimized by surveying the tunneling thickness of the 2.3, 2.6, 2.9, and 3.2 nm SiOxNy layers.