Effect of Electronic Corrections on the Thickness Dependence of Thin Oxide Reliability

The thickness dependence of constant voltage lifetimes tests are compared for ultrathin oxides in the range of 50-125angstroms. An apparent factor of 100 enhancement in the lifetime of 50angstroms oxides relative to the 125angstroms 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 enhancement is removed 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 in thin oxides and that oxide reliability is not affected by thickness down to 50angstroms, depending only on Field. We compare different techniques for determining an effective thickness using current-voltage or capacitance-voltage curves. We show that accurate estimates of the electric field can be obtained from integration of the capacitance-voltage 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.