Thin film properties of tungsten nucleation layers were investigated as a function of SiH4:WF5 flow ratio by Auger electron spectroscopy (AES) depth profiling, thin film x-ray diffraction (XRD), atomic force microscopy (AFM), secondary ion mass spectrometry (SIMS), and resistivity measurements. Tungsten nucleation layers, approximately 1000 Angstrom thick, were deposited on the TiN/Ti glue layer stack at 3:1 and 6:1 SiH4:WF5 flow ratio. The 6:1 flow ratio film gave different film properties compared to the 3:1 film. The AES and XRD results showed that the 6:1 film consists primarily of WSi2, whereas the 3:1 film contains a mixture of W5Si3, WSi2, and possibly W. The AFM analysis indicated that the 6:1 nucleation layer is far smoother and less porous than the 3:1 film, indicating that it is a better diffusion barrier to WF6. The 6:1 films had smaller grains of 100 to 120 nm dimension with uniform distribution. However, the 3:1 films had larger grains of 150 to 190 nm with a bimodal distribution. The 6:1 nucleation is a more robust process to WF6 penetration a conclusion that is further supported by the SIMS data.