NEW INSIGHTS INTO RADIATION-INDUCED OXIDE-TRAP CHARGE THROUGH THERMALLY-STIMULATED-CURRENT MEASUREMENT AND ANALYSIS

An analytic model with no free parameters has been developed which accurately describes thermally-stimulated-current (TSC) measurements spanning more than a factor of 50 in average heating rate. The model incorporates Schottky electric-field-induced barrier lowering and a temperature-dependent ''attempt-to-escape frequency'' equal to approximately 10(14) Hz at 300-degrees-C. Applying this model to TSC measurements provides significantly improved estimates of the energy distribution of trapped holes in irradiated SiO2. All devices examined, including soft and (wet and dry) hard oxides from five process technologies, show similar energy distributions, with a minor peak at approximately 1.2 eV and a broad major peak centered approximately 1.7-2.0 eV above the SiO2 valence band. These energies are closer to photoinjection and tunneling estimates of trapped-hole energy in the literature than previous estimates based on TSC or thermal annealing. We also find that the trapped-electron density in irradiated SiO2 is proportional to the trapped-hole density over a wide range of irradiation conditions. Both the trapped-hole and trapped-electron densities scale with the applied oxide electric field (E(ox)) during irradiation as approximately (E(ox))-1/2. These results strongly support the idea that electrons are trapped at sites associated with trapped holes. Wet gate oxides are found to trap significantly fewer electrons per trapped hole (approximately 16%) than dry oxides (approximately 48%), suggesting that, on average, holes may be trapped closer to the Si/SiO2 interface in the dry oxides than in the wet oxides. Possible models of the trapped-hole/trapped-electron complex are described, and implications for device long-term reliability and annealing response are discussed.