Improving Thermal Stability and Interface State Density of High- $\kappa $ Stacks by Incorporating Hf into an Interfacial Layer on p-Germanium

We propose a new HfGeO
_x
interfacial layer (IL) for the high-κ gate-stacks on p-type germanium substrate with improved thermal stability as compared with that of conventional GeO
_x
IL. We inserted an additional HfO2 layer after the formation of GeO
_x
in the HfO
₂
/Al
₂
O
₃
/GeO
_x
/Ge gate-stack by using plasma-enhanced atomic layer deposition. Through the use of post-deposition annealing and post-metal annealing, the new system exhibited greater thermal immunity and was stable up to 600 °C. We speculate that the improvement originates from the formation of HfGeO
_x
through the combination of HfO
₂
and GeO
_x
, according to the thermodynamic data. By incorporating Hf into interfacial layer, the fabricated high-κ gate-stack with an equivalent oxide thickness of 1.2 nm, a low interface states density (D
_it
) of approximately 3.3×10
¹¹
eV
^-1
cm
^-2
, and an impressive gate leakage current of approximately 2.2 × 10
^-6
A/cm
²
at V
_FB
-1V.