High-Interface-Quality Hf-Based Gate Stacks on Si0.5Ge0.5 Through Aluminum Capping

We fabricated HfO
₂
-based gate stacks on epi-Si
_0.5
Ge
_0.5
substrates and investigated the effect of Al capping on TiN. The results revealed that the Al layer formed Al
₂
O
₃
, which functioned as a barrier against external oxygen diffusion, resulting in excellent interface quality. Furthermore, the density of oxide traps and flat-band voltage could be tuned using various ratios of Al to TiN at the top gate. Thus, an excellent interface state density and equivalent oxide thickness (EOT) of approximately 8
$\times \,\,10^{{10}}$
eV
⁻¹
cm
⁻²
and 1.3 nm were achieved for the gate stack on SiGe through Al capping on TiN.