Effects of Si[sub 3]N[sub 4] Thickness on the Electrical Properties of Oxide-Nitride-Oxide Tunneling Dielectrics

Si O 2 ∕ Si 3 N 4 ∕ Si O 2 tunnel barriers with a residual Si 3 N 4 layer of different thicknesses were fabricated by thermally oxidizing Si 3 N 4 ∕ Si O 2 film. According to leakage current measurements, the effective barrier height was significantly lowered because the Si 3 N 4 middle layer has a lower bandgap than Si O 2 , 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 Si 3 N 4 thickness. For the sample with a distinctive Si 3 N 4 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 Si O 2 ∕ Si interface for the fully oxidized sample resulted in an asymmetric conduction mechanism behavior, which was explained by the band diagram analysis.