Secondary ion mass spectrometry (SIMS) was successfully used as an analytical method to characterize chemical vapor deposited (CVD) tungsten (W) processes. Blanket CVD tungsten film on titanium nitride (TiN) barrier layers generally begins with the deposition of a tungsten nucleation layer by silane (SiH4) reduction of tungsten hexafluoride (WF6), followed by hydrogen (H-2) reduction of WF6, alone to form the bulk tungsten layer. In the present work, the tungsten nucleation layer was formed by simultaneous SiH4, and H-2 reduction of WF6. A two-step Sill, gas flow scheme was used to determine the effects of magnitude and duration of SiH4 flow on the Si concentration at the W/TiN interface. SIMS was used to characterize the Si distribution at the CVD W/TiN interface. SIMS depth profiles indicate, with a constant SiH4 flow time of 3 s, the Si concentration at W/TiN interface does not vary significantly with the increase of SiH4, flow from 20 to 30 seem. However, it increases dramatically with the increase of SiH4, flow from 30 to 48 seem. With a constant SiH4, flow of 40 seem, the Si concentration at the W/TiN interface increases linearly with the increase of the SiH4 flow time. These results amply demonstrate that SIMS analysis can be used to evaluate the deposition process so as to meet the fill and barrier protection requirements for narrow trench or small via.