A new measurement method for trap properties in insulators and semiconductors: Using electric field stimulated trap-to-band tunneling transitions in SiO2

Abstract

A new experimental technique for characterization of traps in insulators and semiconductors and its speed-up derivative are presented which use trap-to-band tunneling emission of electrons. Equations are given which allow the energy levels to be calculated from experimental emission decay data. The expressions are valid for electrically active defects with a discrete energy level or a distribution of levels. The numerical error in calculating the energy level from experimental data is 1%–2% for a given set of energy-band parameters such as the effective masses and the parabolicity of the dispersion relation in the energy gap. The techniques are applied to electron traps in thermally grown integrated-circuit grade SiO2 to illustrate their accurate and utility. An energy distribution of shallow charged oxide traps is found throughout about 0–3 eV below the oxide conduction band edge with a peak density of states at about 0.9 to 1.0 eV. The centroid of the charged oxide traps is about 82 Å from the SiO2/Si interface. The same density–energy curve is observed for oxide traps in many thermally grown dry oxide films thicker than 150 Å. A decrease in the density of the charged oxide traps is found for oxides less than 100 Å. A distribution of capture cross sections versus trap energy depth, ranging from 10−15 to 10−17 cm2, is measured at low oxide electric field (1.1 MV/cm). The shallower traps have a larger capture cross section than the deeper traps. The measured energy level at the peak density is consistent with the recent theoretical anticipation of Robertson and Rudra and Fowler for an oxygen vacancy which relaxes to form a silicon–silicon bond in the oxide [(Si—O)3≡Si—Si≡(O—Si)3].