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 HfO₂ layer after the formation of GeO_x in the HfO₂/Al₂O₃/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 HfO₂ 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 3.3×10¹¹ eV^-1 cm^-2, and an impressive gate leakage current of approximately 2.2×10^-6 A/cm² at V_FBs -1V.