Investigation of transient relaxation under static and dynamic stress in Hf-based gate oxides

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Transient relaxation, which has been addressed as an undesirable issue in high-k alternate gate dielectrics, has been studied systematically. In Hf-based dielectrics, it follows a universal line irrespective of stress times and stress voltages if stressed (static/dynamic) up to certain limits. The results presented here reveal that bulk charge trapping shows a fast transient relaxation (TR) for a very short time (/spl sim/ ms) after stress (substrate injection) followed by a slow relaxation (> 1 s), while interface passivation/relaxation follows a slow trend. Bulk trappings, which play a major role in causing device instabilities in high-k gate oxides, are mostly relaxable, while interface degradation cannot be passivated completely. Moreover, an interface-passivation mechanism seems to be independent of stress histories. Devices with stronger bulk-trapping immunity showed faster TR. The experimental results show good agreement with the simplified mathematical model presented for HfO/sub 2/ gate oxides. The temperature showed a negligible effect in TR.

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