Contamination issues in CVD

The deposition of tungsten by CVD is essentially a catalytic heterogeneous reaction. The tungsten surface acts as the catalyst to activate either the H2 or the SiH4 molecules depending on what chemistry is in use. It is well known from heterogeneous catalysis that extremely low concentrations of surface active contaminants can deactivate the surface and block or slow down the reaction rate. However, it is also possible that certain active molecules can accelerate the deposition once they become adsorbed to the tungsten surface. 

Another problem is that WF6 can become contaminated in the reactor by reaction with stainless steel parts or elastomers. George et al.207 

Hogle et al.209, showed that WF6 will interact with elastomers such as Vespel and Kel-F. The products, detected using infrared absorption spectroscopy, were C02 and CF4. 

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