CVD WSix, films have found widespread use as ultra thin gate, wordline and bitline interconnects due to the lower resistance that polycide offers. For submicron technologies, WSix films based on the monosilane chemistry shows limitations due to the incorporation of high concentrations of Fluorine ions and poor step coverage. Recent work has shown that, WSix films based on the dichlorosilane (DCS) chemistry minimizes these problems. One of the major issues in DCS WSix films is the in-depth compositional non uniformity, especially those deposited on poly-Si substrates. The formation of a W-rich region at the WSix/poly-Si interface can cause localized stresses which can result in cracking and adhesion problems. In this paper, we report the composition and structure of DCS WSix, films deposited on undoped, doped and in situ doped poly-Si and oxide substrates. We have investigated the effect of different processing conditions on Si/W uniformity and the formation of W-rich and Si-rich interfaces, and the role of the nucleation step in modulating the Si/W ratio at the WSix/poly-Si interface. The impact of a Si-rich region at the WSix/poly-Si interface on silicide film properties has also been explored. 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.