Time Dependent Isolation Capability of High Voltage Deep Trench Isolation

The long term isolation properties of deep trenches in thick SOI have been investigated by current-voltage- characteristics. A strong change of the measured trench leakage current was observed depending on the applied voltage. Further on a marked decrease of the leakage current was observed depending on the duration and polarity of the applied stress. The improvement of the formatted trench isolation was found to be irreversible with time, temperature and voltage polarity. This so-called formation effect can be described by a theoretical simulation model assuming a tunneling process of electrons through the oxide barrier, taking into account the charging and discharging of traps within the trench sidewall oxides. The observed formation effect leads to improved reliability results, wherein the trench is either damaged at the start of the stressing or no dielectric breakdown occurs at all.