Analysis of tunnel current through ultrathin gate oxides

Tunnel current through 1.27-8.12-nm-thick gate oxides has been calculated o n the basis of multiple-scattering theory, in which the SiO2 layer is segme nted into multiple rectangular potential barriers. By using the conduction band barrier height of 3.34 eV determined for the SiO2/Si(100) interfaces, a tunneling effective mass of 0.35m(0) is obtained so as to reproduce the S iO2 thickness dependence on the direct tunnel current. The Fowler-Nordheim tunnel current oscillation due to interference between the propagating elec tron wave at the SiO2 conduction band and the wave reflected at the Sio(2)/ Si interface has also been explained by employing an oxide conduction band effective mass of 0.60m(0.) It is found that the oxide thicknesses determin ed by ellipsometry are in good agreement with those extracted by fitting th e measured tunnel current to theoretical one.