New insight on VT stability of HK/MG stacks with scaling in 30nm FDSOI technology

In this paper it is shown that HfO
₂
and HfZrO oxides suffer from large V
_T
instabilities, up to 230mV, when the device width (W) is scaled down to 80nm. It is explained by undesirable lateral oxygen diffusion through the spacers, which mainly modifies the metal workfunction in narrow transistors. HfSiO(N) oxides exhibit a much better immunity to this effect, attributed to a different crystallinity of the HK layer. Moreover, Al incorporation in the gate stack hardly changes the V
_T
stability.