Low-frequency noise in TaSiN/HfO2 nMOSFETs and the effect of stress-relieved preoxide interfacial layer

Low-frequency noise characteristics are reported for TaSiN-gated n-channel MOSFETs with atomic-layer deposited HfO₂ on thermal SiO₂ with stress-relieved preoxide (SRPO) pretreatment. For comparison, control devices were also included with chemical SiO₂ resulting from standard Radio Corporation of America clean process. The normalized noise spectral density values for these devices are found to be lower when compared to reference poly Si gate stack with similar HfO₂ dielectric. Consequently, a lower oxide trap density of ∼4×10¹⁷ cm^-3eV^-1 is extracted compared to over 3×10¹⁸ cm^-3eV^-1 values reported for poly Si devices indicating an improvement in the high-κ and interfacial layer quality. In fact, this represents the lowest trap density values reported to date on HfO₂ MOSFETs. The peak electron mobility measured on the SRPO devices is over 330 cm²/V·s, much higher than those for equivalent poly Si or metal gate stacks. In addition, the devices with SRPO SiO₂ are found to exhibit at least ∼10% higher effective mobility than RCA devices, notwithstanding the differences in the high-κ and interfacial layer thicknesses. The lower Coulomb scattering coefficient obtained from the noise data for the SRPO devices imply that channel carriers are better screened due to the presence of SRPO SiO₂, which, in part, contributes to the mobility improvement.