Nucleation and growth of CVD-W on TiN studied by X-ray fluorescence spectrometry

The initial stage of the chemical vapor deposition (CVD) of W films based on the silane and hydrogen reduction of tungsten hexafluoride has been studied by X-ray fluorescence and Auger depth profiling. Blanket depositions were performed on TiN films with different oxygen content, prepared either by exposing them to atmosphere prior to W process or with the addition of some oxygen during their deposition. The very high sensitivity of XRF was used to obtain quantitative data on films over a wide range of thickness. Two different growth kinetics have been found: up to a very low thickness (of the order of one monolayer) the process is thermally activated while for higher thicknesses the rate does not depend on the W deposition temperature. These results are explained assuming that the thermally activated kinetics is related to the reduction of the titanium oxide layer, which forms at the sample surface after exposure to air, while the other one is related to the W deposition on the already deposited W films.