Low-Frequency Noise Analysis of the Impact of an LaO Cap Layer in HfSiON/Ta2C Gate Stack nMOSFETs

In this work, n-channel MOSFETs with a 0.5 nm LaO cap layer inserted between the 10 nm Ta2C metal gate and the HfSiON gate dielectric have been investigated, with emphasis on the low-frequency noise properties. It is shown that the capped devices show a roughly 0.3 V lowering of the threshold voltage and a significant increase in the maximum transconductance and the low-field mobility. At the same time, it is shown that the 1/f noise spectral density Si is not degraded by the introduction of the cap layer and even a lowering of the noise magnitude for thinner HfSiON layers has been observed. This points to a reduction of the effective gate oxide trap density which could result from the in-diffusion of La in the underlying gate stack.