DETERMINATION OF TUNNELING PARAMETERS IN ULTRA-THIN OXIDE LAYER POLY-SI/SIO2/SI STRUCTURES

In this work the electron tunnelling in device grade ultra-thin 3-6 nm n(+)poly-Si/SiO2/n-Si structures has been analysed. The well known analytic expression for the Fowler-Nordheim tunnelling current was adapted to include the case of direct tunnelling of electrons, which becomes important for oxide layers thinner than 4.5 nm. For these ultra-thin oxide MOS structures it is necessary to take the band bending in the Si substrate and in the poly-Si layer into account to determine the oxide electrical field strength acid to derive the tunnelling parameters of the measured current-voltage characteristic. A method is explained to derive the tunnel barrier height phi(s) and the effective mass of the tunnelling electron m(ox) from the experimental tunnel current characteristics. It is shown that both the direct tunnelling and the Fowler-Nordheim tunnelling current can be quantitatively explained by a WKB approximation using m(ox) as the single fitting parameter.