Reliability of 6-10 nm thermal SiO2films showing intrinsic dielectric integrity

Time-dependent dielectric breakdown (TDDB) of thermally grown 6-10-nm SiO2films in a polysilicon/SiO2/Si structure is studied as a function of electric field (6.7-8.2 MV/cm) and temperature (170-250°C) stressings. Experiments are performed on the SiO2films with no pinholes and no weak oxide spots on dielectric breakdown histograms. TDDB occurrences are characterized by logarithmic normal distribution. The σ values (distribution variance) are found to be 1.0 and 2.0 for 6 and 10-nm SiO2films, respectively. The electric field acceleration factor and activation energy, respectively, are evaluated as 55/(MV/cm) and 1.0 eV for 6-nm films and 80/(MV/cm) and 1.1 eV for 10-nm films. Using these results, the failure rates estimated for 6-10- nm SiO2under an operating condition of 5 MV/cm at 150°C are less than 1 & 10^-11/h for 6-nm films and less than 1 × 10^-9/h for 10-nm films. It is concluded that 1) the 6-10-nm SiO2films with no pinholes and no weak oxide spots are highly reliable with regard to TDDB and 2) thinner (6-nm) oxide is more reliable than thick (10-nm) oxide.