Preparation of low-dielectric-constant F-doped SiO₂ films by plasma-enhanced chemical vapor deposition

The delay due to the dielectric constant of an interlayer film results in the limited performance of very largescale integrated circuits (VLSI). One solution to this problem is the use of a low-dielectric-constant interlayer film such as F-doped SiO₂. We were able to obtain F-doped SiO₂ films with dielectric constants as low as 2.3 and good step coverage by adding CF₄ to SiH₄/N₂O plasma-enhanced chemical vapor deposition (PECVD). Our study focuses on the mechanism of the decrease in the dielectric constant and that of process improvement. It appears that a decrease in the dielectric constant is due to the decrease in the ionic polarization. The change in the Si-O stretching mode due to CF₄ addition seems to be the most important factor in the decrease in the dielectric constant. The improvement of the step coverage and the decrease in the film growth rate are due to the decrease in the sticking probability of the film-forming species.