LOW ELECTRIC-FIELD BREAKDOWN OF THIN SIO2-FILMS UNDER STATIC AND DYNAMIC STRESS

A comprehensive study of Time-Dependent Dielectric Breakdown (TDDB) of 6.5-, 9-, 15-, and 22-nm SiO2 films under de and pulsed bias has been conducted over a wide range of electric fields and temperatures, Very high temperatures were used at the wafer level to accelerate breakdow n so tests could be conducted at electric fields as low as 4.5 MV/cm. New observations are reported for TDDB that suggest a consistent elect ric field and temperature dependence for intrinsic breakdown and a cha nging breakdown mechanism as a function of electric field, The results show that the logarithm of the median-test-time-to failure, log (ta), is described by a linear electric field dependence with a field accel eration parameter that is not dependent on temperature, It has a value of approximately 1 decade/MV/cm for the range of oxide thicknesses st udied and shows a slight decreasing trend with decreasing oxide thickn ess, The thermal activation E-a ranged between 0.7 and 0.95 eV for ele ctric fields below 9.0 MV/cm for all oxide thicknesses, TDDB tests con ducted under pulsed bias indicate that increased dielectric lifetime i s observed under unipolar and bipolar pulsed stress conditions, but di minishes as the stress electric field and oxide thickness are reduced, This observation provides new evidence that low electric field aging and breakdown is not dominated by charge generation and trapping.