THICKNESS DEPENDENCE OF OXIDE WEAROUT

The thickness dependence of thin silicon oxide wearout has been measur ed. The flatband voltages, bulk oxide trap densities, and low-level le akage currents were measured on oxides in the 5 to Il nm thickness ran ge before and after high-voltage stressing. In oxides that had been st ressed at equivalent electric fields for equivalent times, the measure d flatband voltage shifts and stress-generated bulk oxide trap densiti es dropped as the oxide thicknesses dropped and were negligible for ox ides thinner than 6 nm. The low-level pretunneling leakage currents in creased as the oxide thicknesses decreased. In addition to the transie nt, 1/time, tunnel charge/discharge component, a de component to this current appeared as the oxide thicknesses decreased. A model based on uniform trap generation throughout the oxide during the high-voltage s tressing and subsequent tunnel charging and discharging of the traps w ithin approximately 3 nm of either interface after the stress voltages were removed has been used to explain and accurately fit all of the t hickness dependences of the trap generation and flatband voltage shift s. The thickness dependences of the transient and de low-level leakage currents were explained on the basis of electrons tunneling both into , out of, and between the stress-generated traps. Both components of s tress-induced leakage currents were proportional to the stress-generat ed trap densities when the thickness dependences of these currents wer e analyzed.