Effect of electronic corrections on the thickness dependence of thin oxide reliability

The thickness dependence of constant voltage lifetime tests are compared for ultrathin oxides in the range of 50-125 Angstrom. An apparent factor of 100 enhancement in the lifetime of 50 Angstrom oxides relative to the 125 Angstrom oxides is observed at a fixed electric field when the field in the oxide is calculated using the physical thickness of the oxide as determined by ellipsometry. When corrections are made for the distribution of electrons at the silicon interface including depletion in the silicon and quantum-mechanical screening effects then this apparent enhancements is reduced and all oxides have similar lifetimes at a fixed field. Such a rescaling of oxide reliability demonstrates the importance of accurate determination of electric field and oxide voltage in thin oxides and that oxide reliability is not significantly affected by thickness down to 50 Angstrom, depending only on field. We compare different techniques for determining the effective thickness using current-voltage or capacitance-voltage (C-V) curves. We show that accurate estimates of the electric field can be obtained from integration of the C-V relation of the capacitor. When electric fields are calculated using C-V curves, a consistent set of extrapolation parameters can be obtained for all thicknesses. (C) 1997 American Institute of Physics. [S0003-6951(97)04143-0].