Ultrathin refractory metal silicide films, such as tungsten silicide (WSix) offer a wide range of applications in VLSI and ULSI circuits such as local interconnects, bit lines and wordlines. One practical way of depositing WSix is by a CVD technique in which WF6 is reduced by either SiH4 or SiH2Cl2. For sub 0.5 micron technologies, SiH4 based WSix shows limitations due to poor step coverage and high F incorporation (>1020 atoms/cm3 ). If the reducing agent is changed to SiH2Cl2, then these problems are largely eliminated. However, interactions between processing parameters and film properties to achieve compositionally and structurally uniform films are not well understood. In this investigation, SiH2Cl2 based WSix films (60-200 nm) deposited on undoped poly-Si, doped poly-Si and oxide substrates were studied after a high temperature furnace anneal and oxidation cycle. Electron transparent samples were prepared by a low temperature ion beam technique and the individual films of Si-SiO2-poly Si-WxSiy layers were investigated by high resolution cross sectional transmission electron microscopy, x-ray diffraction and electron nanospectroscopy techniques with a beam energy of 300 kV. RBS measurements were used to determine the composition profile through the depth of the film and Si/W uniformity in terms of Si-rich and W-rich interfaces. SIMS measurements were used to determine the impurity content in the silicide film and at the film/substrate interface. This paper focuses on the processing-structure relationships in terms of development of defect structures within WxSiy, the non-stoichiometric W-Si compositons and related crystal structures and the role of the nucleation step in modulating the Si/W ratio at the WSix, /poly-Si interface and discusses their implications on future process development.