Process parameters for low pressure chemical vapor deposition (LPCVD) of selective tungsten to fill vias between aluminummultilevel metallization have been studied.
Stable BCC α-tungsten has been deposited by LPCVD on Al using a gaseous mixture of $WF_6$ and $H_2$, and using a gaseous mixture of $WF_6$, $H_2$ and $SiH_4$.
The thermodynamic calculation and experimental results of Al-reduced tungsten showed the formation of interfacial fluoride compound. But it was demonstrated by AES that high deposition rate can suppress the formation of fluoride at W/Al interface.
Selectivity loss was observed by SEM. It was found that selectivity loss is initiated by-product or intermediate at $H_2$-reduction system. At $SiH_4$-reduction system the slectivity was apt to break regardless of by-product or intermediate.
Excellent step coverage achieved at straight wall vias of high aspect ratio by LPCVD-W.
