Improving Interface State Density and Thermal Stability of High-κ Gate Stack Through High-Vacuum Annealing on Si_0.5Ge_0.5

We fabricated HfO₂-based gate stacks on epi-Si_0.5Ge_0.5 substrates and investigated the effect of thermal treatment on their structural and electrical properties at varying temperatures and pressures in oxygen ambient. The thermal treatment process led to severe degradation of interface quality as the temperature increased. Material analyses indicated that annealing in oxygen ambient resulted in oxygen diffusion from the high-κ material to the SiGe surface, causing undesirable SiGe reoxidation. In high-vacuum annealing, an interface state density of approximately 1.4 × 10¹¹ eV^-1 cm^-2 and a thermal stability of up to 500 °C were achieved for the gate stack on SiGe.