This study investigates the fluorocarbon-based plasma etching (FBPE) of low dielectric constant (ULK) carbon-doped oxide (CDO) films, which have a dielectric constant (k) value of 2.4. The effects of different ion density and ion energy power settings on the chemical composition of the fluorocarbon layer deposited during the etch process were investigated. X-ray photoelectron spectroscopy (XPS) was used to analyse the chemical composition of the post-etched low-k CDO films while spectroscopic ellipsometry (SE) was used to determine the overall film thickness. XPS spectra of the C1s core levels reveal that the relative concentration of CF chi species in the fluorocarbon films reduced as ion density source power and ion energy power levels were increased, and this can be correlated with a higher etch rate and thinner fluorocarbon layer. Plasma conditions which led to the deposition of a thick fluorocarbon film significantly inhibited the etch rate. This work demonstrates that the chemical composition and the thickness of the fluorocarbon film can be controlled by the plasma power parameters, and this has implications for the etching of ULK CDO layers.