Effects of Si₃N₄ thickness on the electrical properties of oxide-nitride-oxide tunneling dielectrics

SiO₂/Si₃N₄/SiO₂ tunnel barriers with a residual Si3 N4 layer of different thicknesses were fabricated by thermally oxidizing Si₃N₄/SiO₂ film. According to leakage current measurements, the effective barrier height was significantly lowered because the Si₃N₄ middle layer has a lower bandgap than SiO₂, which is beneficial in increasing the erasing/programming speed in flash memory devices. However, detrimental effects, such as the increased hysteresis in capacitance-voltage characteristics and the degraded breakdown distribution, were observed due to the significant amount of the charge trapping induced by the increased Si₃N₄ thickness. For the sample with a distinctive Si₃N₄ layer, trap-assisted tunneling and Fowler-Nordheim tunneling were the dominant conduction mechanisms at low and high electric field, respectively. However, the accumulation of N at the SiO₂ Si interface for the fully oxidized sample resulted in an asymmetric conduction mechanism behavior, which was explained by the band diagram analysis.