On the Oxide Trap Density and Profiles of 1-nm EOT Metal-Gate Last CMOS Transistors Assessed by Low-Frequency Noise

The low-frequency noise behavior of replacement metal gate high- k/metal-gate MOSFETs with an equivalent oxide thickness of the SiO₂/HfO₂ bilayer in the range ~ 1 nm has been investigated. It will be shown that both the average trap density and its profile derived from the frequency exponent γ of the flicker noise spectra are mainly determined by the interfacial layer (IL) oxide processing, with a higher trap density corresponding with a thinner chemical oxide, compared with a ≤ 1-nm thermal SiO₂ IL. The thickness of the HfO₂ layer and the metal gate fill has only a marginal impact on the noise power spectral density. It will also be shown that for the extraction of the trap density profiles from the 1/f^γ noise spectra accurate values for the tunneling effective mass and barrier height are required.