Relation between stress-induced leakage current and dielectric breakdown in SiN-based antifuses

Degradation process of metal-to-metal antifuses which use thin silicon nitride as dielectric layer under high field stress is studied in detail. Prior to dielectric breakdown, leakage current at stress voltage increases with large and complex fluctuations for any sample. So-called stress-induced leakage current at low voltages in current-voltage characteristics is also observed and it increases as the stress continues. It is shown that the stress-induced leakage current and the pre-breakdown leakage current with fluctuations are identical phenomena, and that the stress-induced leakage current strongly relates to the dielectric breakdown. Therefore,it is important to understand the mechanism of the stress-induced leakage current in order to improve antifuse reliabilities. Discrete two-step fluctuations on the stress-induced leakage currents at low voltages are found and the stress-induced leakage current is not proportional to antifuse areas. Considering these findings, it is concluded that the stress-induced leakage current flows through local spots. The conduction mechanism of the stress-induced leakage currents is also studied. The main conduction process in SiN films appears to be Frenkel-Poole conduction. We also find that as the stress continues, the barrier height between an electrode and a SiN film becomes lower and the dielectric constant becomes larger. It is also found that the appearance of the stress-induced leakage current in the I-V characteristics depends on the thickness of the barrier metal. Dielectric breakdown electric field and TDDB lifetime also show the same dependence. Considering the experimental results, the stress-leakage current is related to the electrode material.<>