Correcting interface-state errors in MOS doping profile determinations

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It is shown that the apparent doping profile obtained from a 1/CHF2 vs V plot (where CHF is the high-frequency MOS capacitance and V is the voltage across the capacitor) can be corrected for interface-state effects to obtain a more accurate doping profile. This more accurate doping density, N(w), at distance w from the semiconductor-insulator interface is related to the uncorrected density, N0(w), obtained by neglecting interface states, by N(w)=N0(w) (1−CLF/Cox) (1−CHF/Cox)−1, where CLF is the quasistatic MOS capacitance at the voltage corresponding to the depletion width w and Cox is the oxide capacitance. This scheme is shown to provide the doping profile to within 5% accuracy for distances from three extrinsic Debye lengths out to the maximum depletion width obtainable in thermal equilibrium. Experimental verification of this method is obtained by measuring the doping profile on a single capacitor before and after bias-temperature stress. The same doping profile is obtained in both cases despite a large change in interface-state density.