Low-frequency noise characteristics for various ZrO₂-added HfO₂-based 28-nm High-k/metal-gate nMOSFETs

In this letter, the effect of adding ZrO₂ to different positions in an HfO₂-based high-k (HK) gate-stack is investigated by a low-frequency (1/ f ) noise measurement. The tested nMOSFETs are fabricated using 28-nm gate-last HK/metalgate technology with a ∼1-nm SiO₂ interfacial layer. The 1/ f noise mechanism of these devices is described by the carrier number fluctuation, and the extracted trap densities (Nt) are 8.9 × 10¹⁸- 5.1 × 10¹⁹ eV^-1 cm ^-3. However, reference devices with a pure ZrO₂ gate dielectric exhibit 1/ f noise characteristics that are consistent with the unified model, which incorporates both the carrier number and the correlated mobility fluctuations. The reference devices are with lower N_t values in the range of 5.8 × 1017 - 2.4 × 10¹⁸ eV^-1 cm^-3. In addition, there is an increase in N_t as the initial HfO₂ layer becomes thicker. These results show that the trapping behavior is mainly dominated by the HfO₂ film and is dependent on the thickness of the initial HfO₂ layer in the ZrO ₂/HfO₂/SiO₂ gate-stack.