Improving Interface State Density and Thermal Stability of High-kappa Gate Stack Through High-Vacuum Annealing on Si0.5Ge0.5

Abstract

We fabricated HfO2-based gate stacks on epi-Si0.5Ge0.5 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-k material to the SiGe surface, causing undesirable SiGe reoxidation. In high-vacuum annealing, an interface state density of approximately 1.4 x 10(11) eV(-1) cm(-2) and a thermal stability of up to 500 degrees C were achieved for the gate stack on SiGe.