Charge storage and distribution in the nitride layer of the metal-nitride-oxide semiconductor structures

Electronic charge trapping in the low-pressure chemically vapor deposited thin film of Si3N4 has been investigated by internal photoelectric-effect technique. Charge-storage characteristics and the spatial distribution of electrons trapped in the Si3N4 layer of a biased Al-Si3N4-SiO2-Si structure have been determined using photocurrent and high-frequency C-V measurements. Electrons generated by internal photoemission at the Si surface were captured by traps located within the Si3N4 layer which gave rise to a charge-storage mechanism. Some of these trapped charges were then photoionized by photons with an energy of 4.14 eV and removed from the insulator. This resulted in a discharging mechanism. The flatband voltage shifts for various charging and discharging processes were determined and characterized in detail. The total trapped electronic charge was on the order of 3.14×1012/cm2, with a retention time of 48 days in the dark. The etch-back experiments, where the charged Si3N4 layer was etched back in steps, determined the distribution of the trapped electronic charge across the Si3N4 film of the metal-nitride-oxide semiconductor structure. The midfilm concentration of these trapped electrons was 2.8×1017/cm3.