Electron tunneling through ultrathin SiO2

The tunnel current through 3.0–6.0 nm thick SiO2 grown on Si(100) substrates has been compared with the theory of the WKB approximation. By using the measured conduction band barrier height, the electron effective mass, which is only the fitting parameter, is obtained to be (0.34 0.04)m0 in the Fowler-Nordheim tunneling region and (0.29 0.02)m0 in the direct tunneling region. It is also shown that the charge-to-breakdown for electron injection from n+ poly-Si gates is not significantly deteriorated by decreasing the oxide thickness to 3.3 nm and even dramatically improved for the case of a 3.0 nm thick gate oxide. Quasi-breakdown current observed in ultrathin SiO2 has been analyzed and a new dielectric degradation model is proposed.