In Situ Process Control of Trilayer Gate-Stacks on p-Germanium With 0.85-nm EOT

In situ spectroscopic ellipsometry was utilized in an atomic-layer-deposition (ALD) reactor for rapid and rational gate stack process optimization of the trilayer dielectric HfO
₂
/Al
₂
O
₃
/GeO
_x
on Ge. The benefit of this approach was demonstrated by developing an entire process in situ: 1) native oxide removal by hydrogen plasma; 2) controlled reoxidation for Ge surface passivation; and 3) deposition of Al
₂
O
₃
and HfO
₂
using thermal ALD. The low-k layer thicknesses were scaled down without losing their respective functions, i.e., GeO
_x
to form an electrically well behaved interface with Ge and Al
₂
O
₃
to thermodynamically stabilize the GeO
_x
/Ge interface. Aggressive equivalent-oxide-thickness scaling of the trilayer stack down to 0.85 nm with a low gate leakage of 0.15 mA/cm
²
at V
_FB
- 1 V was achieved, while preserving a high-quality dielectric-semiconductor interface.