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

We propose a new HfGeOx interfacial layer (IL) for the high-κ gate-stacks on p-Type germanium substrate with improved thermal stability as compared with that of conventional GeOx IL. We inserted an additional HfO ₂ layer after the formation of GeO _x in the HfO ₂ /Al ₂ O ₃ /GeOx/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 (Dit) 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 _FBs -1V.