Tunneling Transport and Reliability Evaluation in Extremely Thin Gate Oxides

Direct tunnel current through n+poly-Si /1.6 to 4.8nm thick SiO2/p-Si(100) structures has been calculated on the basis of the WKB approximation. The measured current versus oxide voltage characteristics are well explained by the theory with the only one fitting parameter which is the tunneling electron effective mass m*DT = (0.29±0.02)m0 independent of the oxide thickness. It is found that the quasi-breakdown of the oxides under constant current stressing in the direct tunneling regime is accompanied with multivalued gate-voltage fluctuations, indicating dynamic growth or shrinkage of a conducting filament near the SiO2/Si interface. The areal size and length of the filament are evaluated from the analysis of the stress-induced leakage current. The charge to breakdown for oxides thinner than 3 nm exceeds 104C/cm2 at an oxide field strength of 17 MV/cm.