High Performance Ge pMOSFETs With HfO2/Hf-Cap/GeOx Gate Stack and Suitable Post Metal Annealing Treatments

An equivalent oxide thickness of ~0.53 nm, gate leakage current density of
$\sim 10^{-4}\text{A}$
/cm
²
at
V

_FB
+ 1 V,
I
_ON
/
I
_OFF
ratio of
$10^{\text {4}}$
, subthreshold swing of 136 mV/dec, and peak hole mobility of 375 cm
²
/V-s at
N

$_{\text {inv}} = 1.6 \times 10^{12}$
cm
⁻²
in Ge p-type metal–oxide–semiconductor-field-effect transistors (pMOSFETs) are achieved by HfO
₂
/Hf-cap/GeO
_x
gate stack with suitable post-metal-annealing (PMA) treatments. Such a high mobility in Ge pMOSFETs can be attributed to an ultrathin GeO
_x
layer at the surface of Ge substrate. Ge
⁺
and Ge
⁺²
in GeO
_x
layer are re-oxidized to higher oxidation state by gettered oxygen, which is captured by Hf-cap from GeO
_x
and HfO
₂
during PMA. The minimized contents of Ge
⁺¹
and Ge
⁺²
in GeO
_x
are crucial to achieve excellent electrical characteristics.