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

Abstract

We propose a new HfGeOx interfacial layer (IL) for the high-kappa 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 GeOx 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 degrees C. We speculate that the improvement originates from the formation of HfGeOx through the combination of HfO2 and GeOx, according to the thermodynamic data. By incorporating Hf into interfacial layer, the fabricated high-kappa gate-stack with an equivalent oxide thickness of 1.2 nm, a low interface states density (D-it) of approximately 3.3 x 10(11) eV(-1) cm(-2), and an impressive gate leakage current of approximately 2.2 x 10(-6) A/cm(2) at VFB-1V.