Tungsten film has been deposited by a low pressure chemical vapor deposition (LPCVD) on silicon single crystal using a gaseous mixture of $WF_6$ and Ar, and using a gaseous mixture of $WF_6$, $H_2$, and $SiH_4$.
The deposition mechanism of the tungsten film deposited by the silicon reduction of $WF_6$ using the gaseous mixture of $WF_6$ and Ar has been studied by investigating the effects of deposition temperature on the deposited tungsten thickness and on the deposition reaction time. The tungsten film was found to have a structure of porous $\alpha$-tungsten, and to have a self limiting thickness phenomenon. The self limiting thickness reaches a maximum of 700 $\mbox{\AA}$ at the deposition temperature of 335℃, and the deposition reaction time decreases with the deposition temperature. It is believed that the blocking action of a tungsten subfluoride produced by the incomplete reduction of $WF_6$ results in the self limiting thickness phenomenon.
The deposition mechanisms of tungsten film deposited by $SiH_4$ reduction of $WF_6$ using the gaseous mixture of $WF_6$, $H_2$, and $SiH_4$ have been studied by analysing the effects of deposition variables on the deposition rate. The experimental results show that the deposition rate is controlled by surface reaction rates. The deposition rate increases with the $WF_6$, and $SiH_4$ partial pressure at $WF_6$ partial pressure lower than 0.1 torr. However the deposition rate is independent of $WF_6$ partial pressure, and increases with $SiH_4$ partial pressure at $WF_6$ partial pressure higher than 0.1 torr.
The effects of the deposition variables on the electrical properties and the possibility of the selective deposition of tungsten film have also been studied. The electrical resistivity of tungsten film produced by the $SiH_4$ reduction of $WF_6$ has a minimum of 8 $\mu\Omega$ cm, and it increases with the deposition temperature, and with the $SiH_4/WF_6$ input ratio. It was found that the low pressure chemical vapor deposition of tungsten films using the gaseous mixture of $WF_6$, $H_2$, $SiH_4$ can be applied to the selective deposition of tungsten films. The selectivity of the tungsten film is enhanced by decreasing the deposition temperature and the $SiH_4/WF_6$ input ratio.
