The downscaling of complementary metal-oxide semiconductor transistors requires new materials such as Ge substrates for high carrier mobility and high-k dielectrics to decrease the equivalent oxide thickness while reducing the leakage current from the channel to the gate. Photoemission and Auger electron spectroscopies are used to investigate the interfaces of the W/HfO2/GeON/Ge stack. Hard x-ray photoemission spectroscopy is also used to achieve bulk sensitivity. The GeON thin interfacial layer is obtained by nitridation of the germanium native oxide. Nitridation at 480 degrees C and 120 mbars yields the highest nitrogen incorporation (nearly 20 at. %). X-ray photoemission spectroscopy analysis shows the presence of Ge-Hf bonding states, indicating direct interaction between the germanium and the hafnium oxide despite the GeON passivating layer. High energy photoemission is used to probe the buried W/HfO2 interface. No interfacial layer such as WO, is observed between W and HfO2. (c) 2007 American Vacuum Society.