Integration of NiSi, based fully silicided metal gates with HfO2, high-k gate dielectrics offers promise for fiirther scaling of complementary metaloxide- semiconductor devices. A combination of high resolution transmission electron microscopy and small probe electron energy loss spectroscopy (EELS) and energy dispersive X-ray analysis has been applied to study interfacial reactions in the undoped gate stack. NiSi was found to be polycrystalline with the grain size decreasing from top to bottom of NiSi, film. Ni content varies near the NiSi/HfOx. interface whereby both Ni-rich and monosilicide phases were observed. Spatially non-uniform distribution of oxygen along NiSix/HfO2 interface was observed by dark field Scanning Transmission Electron Microscopy and EELS. Interfacial roughness of NiSix/HffO(x)was found higher than that of poly-Si/HfO2 likely due to compositional non-uniformity, of NiSix No intermixing between Hf, Ni and Si beyond interfacial roughness was observed. (c) 2007 Elsevier B.V. All rights reserved.