Fluorine-doped plasma-enhanced chemical vapour deposition (PECVD) tetraethylorthosilicate (TEOS) SiO2 thin film was investigated for improvement in gap-filling capability as an inter-metal dielectric. Both C2F6 and triethoxyfluorosilicate (TEFS) were evaluated as fluorine (F) dopants. Both kinds of F-doped films provided significantly better gap-filling capability than undoped films. This was attributed to the good bottom-step coverage and preferential sidewall etching due to the presence of F. However, there was a markedly different relationship between gap-filling capability and F concentration for the two dopant precursors. Finally, it was shown that either C2F6 or TEFS doping can extend the gap-filling capability of SiO2 down to 0.35 mu m metal spacing with an aspect ratio of 2.0:1.