Accurate measurement of trivalent silicon interface trap density using small signal steady-state methods

Abstract

The high–low-frequency capacitance method for determining the interface trap density is widely used in studying the effects of ionizing radiation on thermally grown SiO2, and in verifying the trivalent silicon interface traps first discovered in electron paramagnetic resonance studies. It is shown that the high–low-frequency capacitance method gives fictitious interface trap density peaks because of the departure of the 1-MHz high-frequency capacitance from the ideal high-frequency capacitance. This method gives accurate values of the interface trap density near the center of the silicon band gap, but for a given high frequency, the range of band-gap energy over which accurate values are obtained decreases with increasing interface trap density. Interface trap density is obtained over a band-gap energy range with an accuracy that is independent of interface trap density from a comparison of the measured and calculated slopes of gate bias versus equilibrium band-bending curves using the Q-C (charge-capacitance) method. The accuracy of this method is verified using the conductance method. This work shows that it is not likely that interface traps are trivalent silicon defects superimposed on a U-shaped background interface trap distribution of unknown identity.