The nature of intrinsic hole traps in thermal silicon dioxide

The energy and spatial distribution of intrinsic hole traps in dry thermal silicon dioxide have been determined. Thermal detrapping was used for the determination of energy levels of the traps and the etch-back technique was used to find the spatial location of the traps. These traps are distributed in energy from 1.0 to 1.5 eV with respect to the valence band edge of the silicon dioxide. Their centroid is located at approximately 120 Å from the Si–SiO2 interface. Results of various postoxidation annealing treatments show that the density of traps is significantly dependent on the process conditions. Like fixed charge Qf, these traps seem to be related to the lattice imperfections in SiO2 near the interface; however, the hole trap density and Qf vary in opposite directions due to the process changes. N2 annealing increases the trap density and O2 annealing, which reduces the hole trap density, increases the electron trap density in SiO2. Based on these results we support the trivalent silicon model for the traps and we postulate that nonbridging oxygen acts as an electron trap in SiO2. These results also support Raider and Berman’s model for fixed charge Qf.