Observation of latent reliability degradation in ultrathin oxides after heavy-ion irradiation

Constant voltage time-dependent-dielectric-breakdown distributions were obtained for both unirradiated and irradiated 3.0 and 3.2 nm thick SiO ₂ films subjected to ⁶⁰Co gamma irradiation and heavy ions of 823 MeV ¹²⁹Xe (linear energy transfer=59MeV-cm²/mg). The gamma irradiation had no effect on oxide lifetime. The heavy ion irradiation substantially reduced oxide life even though the devices were biased at 0.0 V during irradiation. The reduction of oxide lifetime under constant-voltage stress conditions was a strong function of the heavy ion fluence.