The effect of interfacial reactions on the electrical properties of a polycrystalline (poly) Si1-xGex/HfO2 gate stack were evaluated in terms of annealing conditions and the results were compared with those of a conventional poly-Si/HfO2 system. In the poly-Si0.4Ge0.6/HfO2 gate stack, silicate formation was the dominant reaction at the poly-Si0.4Ge0.6/HfO2 interface after annealing at 900 °C, resulting in the significant decrease in leakage current. From x-ray photoelectron spectroscopy analysis, the binding states of Hf silicates were clearly observed at a binding energy of about 16.1 eV in Hf 4f spectra and 102.7 eV in Si 2p spectra. However, in the poly-Si/HfO2 gate stack, the accumulation capacitance became undeterminable and the leakage current increased suddenly after annealing at 900 °C due to silicide formation at the poly-Si/HfO2 interface. The differences in reactions between a poly-Si/HfO2 interface and a poly-Si0.4Ge0.6/HfO2 interface are attributed to the accumulation of Ge. © 2003 American Institute of Physics.