Tungsten films have been deposited on the silicon single crystal by a low pressure chemical vapor deposition (LPCVD) using a gaseous mixture of $WF_6$, $H_2$ and He.
The deposition mechanism of the tungsten films produced by the hydrogen reduction of $WF_6$ has been studied by investigating the effects of deposition variables on the deposition rate. The experimental results show that the deposition rate is controlled by the surface reaction having an activation energy of about 15.4 Kcal/mole. The reaction order for $WF_6$ is one-sixth and the reaction order for $H_2$ is one-half. The rate limiting step is suggested to be the desorption of HF molecules adsorbed on the substrate.
The effects of the deposition variables on the electrical resistivity and the selective property of the deposited tungsten films have also been studied. The electrical resistivity of the deposited tungsten films decreases with increasing the film thickness and has a constant value of 9.5μ$\Omega$ cm above the films thickness of 10000 A, and it is independent of the deposition temperature and the $WF_6/H_2$ input ratio. The selectivity of the deposited tungsten films deteriorates on increasing either the deposition time or the deposition temperature.
