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 HfO₂/Al₂O₃/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 Al₂O₃ and HfO₂ 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 Al₂O₃ 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/cm² at V_FB-1 V was achieved, while preserving a high-quality dielectric-semiconductor interface.