Thermal Stability and Structural Characteristics of (Zr_0.6Al_0.4)O_1.8 Thin Film on Strained SiGe Layer

It is well known that the hole mobility is greatly enhanced in compressively strained SiGe layers deposited on Si. However, the use of SiGe in mainstream metal-oxide-semiconductor field effect transistors (MOSFET) has been plagued by the poor gate oxides due to the Ge segregation and serious degradation of the oxide properties during conventional thermal oxidation of the strained SiGe layers. In advanced MOSFET devices, the aggressive down-scalingof the gate oxide thickness has led to considerable interest in high-permittivity (high-K) materials having low leakage current, high thermal stability, and good interface properties comparable to the Si/SiO₂ interface. In this paper, we report on the microstructure properties of high-K Zr_0.6Al_0.4O_1.8 film fabricated directly on strained-SiGe substrates by ultra-high vacuum electron-beam evaporation (UHV-EBE) and then annealed in N₂ at various temperatures. X-ray diffraction (XRD) reveals that the onset crystallization temperature of the Zr_0.6Al_0.4O_1.8 film is about 900°C that is 400°C higher than that of pure ZrO₂. The ~12 nm thick amorphous Zr_0.6Al_0.4O_1.8 film and the ~3 nm thick amorphous interfacial layer (IL) are studied by high-resolution transmission electron microscopy (HRTEM). Our results show that there is no undesirable amorphous phase separation during annealing at temperatures below and equal to 800°C in the Zr_0.6Al_0.4O_1.8 film. X-ray photoelectron spectroscopy (XPS) reveals that zirconium and aluminum are both in the fully oxidation states. The secondary ion mass spectrometry (SIMS) results indicate the formation of a nonstiochiometric silicate network and a Zr-doped SiO₂ or Zr-silicate phase at the Zr_0.6Al_0.4O_1.8/SiGe interface. Zr_0.6Al_0.4O_1.8 is thus a promising gate dielectric in next-generation SiGe-based microelectronic devices, especially at high temperature.