BREAKDOWN YIELD AND LIFETIME OF THIN GATE OXIDES IN CMOS PROCESSING

The processing effects on thin gate oxide yield and lifetime were studied by using ramp voltage and time-dependent dielectric breakdown (TDDB) measurements on minimally processed MOS capacitors and fully processed devices in a CMOS technology. Gate oxides grown in a wet ambient are considerably superior to those grown in a dry O2 ambient interms of breakdown distribution, yield, and lifetime. CMOS technology on the gate oxide breakdown characteristics are examined. Fully processed CMOS devices show a large reduction in gate oxide yield and lifetime as compared to minimally processed capacitors. Additional processing for double level metallization further degrades the gate oxide. This result indicates the cumulative nature of processing induced damage. Breakdown characteristics are significantly degraded when electrons are injected from the polysilicon gate as opposed to injection from the silicon substrate for the fully processed devices. This polarity dependence can be explained by plasma processing induced trapped holes near the polysilicon/SiO2 interface which also cause anomalous leakage currents with a negative gate bias.