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 $V_{\rm FB}$ –1 V was achieved, while preserving a high-quality dielectric-semiconductor interface.