Deposition and surface modification of SiOf films with low dielectric constant

Abstract

Low dielectric constant fluorine-doped silicon dioxide (SiOF) films were deposited using electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECRPECVD) with SiF4 and O2 as source gases. The effect of fluorine addition on the dielectric properties of the film as a function of the SiF4/O2 gas flow ratio is described in this paper. Also, the effect of post-plasma treatment on the moisture absorption of SiOF films for IMD materials in multilevel interconnections of ultra-large scale integrated circuits (ULSIs) was investigated. The SiOF film deposited at an SiF4/O2 gas flow ratio of 1.0 exhibited a fluorine content of 11.8 at.% and a dielectric constant of 3.14. When the duration time of post-plasma treatment increased, the following results were obtained: The etch rate of SiOF films decreased from 80 A/sec to 10 A/sec, and surface roughness of the plasma-treated SiOF films increased in relation to the ion bombardment effect of the plasma. The refractive index and relative dielectric constant increased from 1.391 to 1.461 and from 3.14 to 3. 90, respectively, due to the changes of surface chemistry in post-plasma treatment. The leakage current density of SiOF films prepared by ECRPECVD using SiF4 and O2 was less than 1 x 10-9 A/cm2 and the breakdown field strength increased from 3.5 MV/cm to 8 MV/cm.