Physical analysis of Ti-migration in 33 Å gate oxide breakdown

Abnormal titanium migration in the poly-Si gate and transistor channel near the source/drain extension was discovered in Ti-silicided 0.18 × 0.40 μm² MOSFETs after constant voltage stress of 5.1 V at 100°C during gate dielectric breakdown study. Coupled with a soft breakdown event, lateral titanium migration from the source/drain active Si regions and titanium downward protrusion within the poly-Si gate take place. This leads to a Ti-silicide migration induced enhanced junction leakage and a degraded transistor performance. Even though the transistor still functions electrically, this new degradation phenomenon may lead to early failure in the device, posing a reliability concern. We postulate that the abnormal titanium migration was triggered by an enhanced localized current density induced through the breakdown spot in the gate dielectric, leading to an extraordinary titanium migration due to the presence of the high magnitude of electrical driving force. We call this new mechanism dielectric breakdown induced-silicide migration (DBIM). A similar phenomenon has not been observed so far in cobalt-silicided 0.15 μm transistor fabricated with 25 Å gate oxide.