Charge trapping and TDDB characteristics of ultrathin MOCVD HfO2 gate dielectric on nitrided germanium

Abstract

In this letter, we investigate the long-term reliability characteristics of ultrathin HfO2 dielectrics on nitrided germanium for the first time. Stress-polarity dependence in charge trapping and time-dependent dielectric-breakdown (TDDB) characteristics has been observed in germanium n- and p-type devices. The p-MOS devices exhibit severe charge trapping under stress, while no significant charge trapping and stress-induced leakage current were found in the n-MOS devices. In terms of operation-voltage projection for a ten-year lifetime, Vg = 2.8 and -2.1 V is projected for the germanium p- and n-MOS devices, respectively, with an equivalent oxide thickness of 11 Å. Compared to Si control samples, germanium devices show a comparable projected operation voltage, indicating that the TDDB for high-κ dielectrics on nitrided germanium is not a concern. The stress-polarity dependence in germanium devices is believed to result from the asymmetrical band structure and the significant difference of the electric field strength across the gate dielectric between the positive and negative stress conditions. © 2007 IEEE.