Low-Frequency Noise Characteristics for Various ZrO₂-Added HfO₂-Based 28-nm High-k/Metal-Gate nMOSFETs

In this letter, the effect of adding ZrO2to 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/metal-gate technology with a ~ 1-nm SiO2interfacial layer. The 1/fnoise mechanism of these devices is described by the carrier number fluctuation, and the extracted trap densities (Nt)are 8.9 × 1018-5.1 × 1019eV-1cm-3. However, reference devices with a pure ZrO2gate dielectric exhibit 1/fnoise characteristics that are consistent with the unified model, which incorporates both the carrier number and the correlated mobility fluctuations. The reference devices are with lowerNtvalues in the range of 5.8 × 1017-2.4 × 1018eV-1cm-3. In addition, there is an increase inNtas the initial HfO2layer 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 HfO2layer in the ZrO2/HfO2/SiO2gate-stack.