HOT-CARRIER-DEGRADATION CHARACTERISTICS FOR FLUORINE-INCORPORATED NMOSFETS

Hot-carrier-degradation characteristics for nMOSFET’s incorporating fluorine in the gate oxide have been studied. Fluorine was implanted into the polysilicon gate, followed by 1000°C annealing to diffuse fluorine into the gate oxide. Transconductance (gm) for the devices with high dosages of fluorine implantation decreased linearly in stress time, while gm for devices without fluorine and with low implantation dosages decreased by almost the square root of stress time. Device lifetime, defined as 10% gm reduction, for devices implanted with high dosages of fluorine was shorter at high drain voltage stress than that for those without or with low dosage of fluorine, but longer at low voltage stress. As to the relationship between device lifetime and substrate current, the fluorine-incorporated device had higher critical energy to create interface traps by hot-carrier injection than the device without fluorine. High-temperature annealing in hydrogen ambient increased device degradation. However, the fluorine incorporation had the advantage of hot-carrier immunity for the hydrogen annealing. © 1990 IEEE