Plasma deposition of low-dielectric-constant fluorinated amorphous carbon

Abstract

Fluorinated amorphous carbon thin films (a-C:F) for use as low-dielectric-constant interlayer dielectrics are deposited by helicon-wave plasma enhanced chemical vapor deposition. To improve their thermal stability, the feasibility of adjusting the fluorine-to-carbon (F/C) ratio by changing the deposition pressure was investigated. Decreasing the pressure increased the dissociation of a source fluorocarbon material in the plasma and decreased the F/C ratio of the deposited film. Both the thermal stability and the dielectric constant of the a-C:F films were increased as the F/C ratio was decreased. Thus, there is a tradeoff relationship between a low dielectric constant and high thermal stability and the tradeoff could be optimized by the pressure during deposition. The mechanism of the pressure dependency of the dielectric constant of a-C:F films was investigated by quantifying the contribution of each polarization and found that a decrease in the dielectric constant of a-C:F films can be attributed to decreases in the orientational and electronic polarizations.