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A replacement gate process employing a HfN dummy gate and sub-1-nm equivalent oxide thickness (EOT) HfO2 gate dielectric is demonstrated. The excellent thermal stability of the HfN-HfO2 gate stack enables its use in high temperature CMOS processes. The replacement of HfN with other metal gate materials with work functions adequate for n- and pMOS is facilitated by a high etch selectivity of HfN with respect to HfO2, without any degradation to the EOT, gate leakage, or time-dependent dielectric breakdown characteristics of HfO2. By replacing the HfN dummy gate with Ta and Ni in nMOS and pMOS devices, respectively, a work function difference of ∼0.8 eV between nMOS and pMOS gate electrodes is achieved. This process could be applicable to sub-50-nm CMOS technology employing ultrathin HfO2 gate dielectric.
Date of Publication: Aug. 2004