Impact of the gate-electrode/dielectric interface on the low-frequency noise of thin gate oxide n-channel metal-oxide-semiconductor field-effect transistors

The low-frequency (LF) noise of n-MOSFETs with a 1.5 nm SiON gate oxide is studied for different gate materials, namely, a polycrystalline (poly) silicon gate, a fully nickelsilicided (FUSI) gate and a NiSi FUSI gate deposited on 10 cycles of HfO₂. The principal aim is to identify the most likely origin of the predominant 1/f noise in the thin gate oxide devices by investigating the impact of the gate electrode processing. It is reported that the lowest input-referred voltage noise spectral density (S_VG) in linear operation for a gate voltage at the threshold voltage is found for the FUSI transistor, while adding 10 cycles of HfO₂ enhances markedly the noise magnitude. The 1/f noise characteristic behaves according to the number fluctuations theory so that the results are interpreted in terms of trapping and de-trapping of channel carriers by defects in the gate dielectric layer. Therefore, the marked effect of the gate material is at present ascribed to the different trap density in the vicinity of the gate-SiON interface, which is derived from the LF noise spectra.