Hot-carrier-degradation characteristics for fluorine-incorporated nMOSFET's

Fluorine was implanted into the polysilicon gate and diffused into the gate oxide by annealing at 1000 degrees C. Transconductance (g/sub m/) for the devices with high dosages of fluorine implantation decreased linearly in stress time, while g/sub m/ for devices without fluorine and with low implantation dosages decreased by almost the square root of stress time. Device lifetime, defined as 10% g/sub m/ 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.<
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