Dielectric breakdown induced epitaxy in ultrathin gate oxide - a reliability concern

Breakdowns in ultrathin gate oxide (Gox) ranging from 16-33 /spl Aring/ were physically analyzed with transmission electron microscope after constant voltage stress. In the Gox of 25 and 33/spl Aring/, a dielectric breakdown induced epitaxy (DBIE) at the gate oxide region is detected for compliance current of 100 nA and above, regardless of breakdown hardness. The compliance current for the transition of soft breakdown (SBD) to hard breakdown (HBD) is found to be in the range of 10-100 /spl mu/A, whereas for the thinner Gox of 16 /spl Aring/, the upper compliance current limit of SBD to HBD is greatly reduced to around 1 - 10 /spl mu/A and SBD DBIE is hardly detected. The results clearly indicate that DBIE is always present in the HBD oxides regardless of its thickness. Its presence in the SBD oxides is an indication of the early stage of catastrophic failure process that poses a Gox reliability concern.